Fix a NULL pointer exception when main exynos drm driver was probed
successfully but no components were added (e.g. by incomplete DTS). In
such case the exynos_drm_load() is never called and drvdata is NULL.

The NULL pointer exception may theoretically also happen as a effect of race between
adding components and main driver: if suspend of the driver happens
before adding components.

Trace:
[    1.190295] [drm] Initialized drm 1.1.0 20060810
[    1.195209] exynos-drm-ipp exynos-drm-ipp: drm ipp registered successfully.
(...)
[   24.001743] PM: Syncing filesystems ... done.
[   24.002177] Freezing user space processes ... (elapsed 0.000 seconds) done.
[   24.007403] Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
[   24.032559] Unable to handle kernel NULL pointer dereference at virtual address 00000134
[   24.035007] pgd = dedd8000
[   24.037734] [00000134] *pgd=5ee13831, *pte=00000000, *ppte=00000000
[   24.043953] Internal error: Oops: 17 [#1] PREEMPT SMP ARM
[   24.049329] Modules linked in:
[   24.052371] CPU: 0 PID: 1 Comm: sh Not tainted 3.16.0-rc3-00035-geba20bbdde04-dirty #51
[   24.060354] task: df478000 ti: df480000 task.ti: df480000
[   24.065743] PC is at mutex_lock+0x10/0x50
[   24.069733] LR is at drm_modeset_lock_all+0x30/0xbc
[   24.074590] pc : [<c048516c>]    lr : [<c02a14b4>]    psr: a0000013
[   24.074590] sp : df481db8  ip : 00000000  fp : c05e524c
[   24.086045] r10: 00000002  r9 : c02c1fe4  r8 : deca5e44
[   24.091253] r7 : 00000000  r6 : 00000000  r5 : 0000014c  r4 : 00000134
[   24.097763] r3 : 00000000  r2 : 00000000  r1 : 00000000  r0 : 00000134
[   24.104275] Flags: NzCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment user
[   24.111391] Control: 10c53c7d  Table: 5edd806a  DAC: 00000015
[   24.117120] Process sh (pid: 1, stack limit = 0xdf480240)
[   24.122502] Stack: (0xdf481db8 to 0xdf482000)
[   24.126843] 1da0:                                                       dee01d80 c02a14b4
[   24.135004] 1dc0: 00000000 00000000 c07aff98 c02aec7c 00000002 00000000 00000000 c07aff98
[   24.143164] 1de0: deca5e10 c02aecf4 c02aecd4 c02c2010 00000000 c02c9470 00000000 00000000
[   24.151322] 1e00: 00000000 00000000 deca5e10 deca5e10 00000000 c07aff98 00000002 deca5e44
[   24.159482] 1e20: c06d8f78 c06fb800 deca5e78 c02ca660 df7baf00 007b0aa0 deca5e10 c06fb7c8
[   24.167641] 1e40: c07aff98 00000000 00000002 c02cbe18 9757aec5 00000005 9757aec5 00000005
[   24.175801] 1e60: ded1d380 00000003 00000003 c05c74d8 ded1d380 c07209d4 c05c7514 c07105d8
[   24.183960] 1e80: 01e2a738 c0068a74 00000000 c05c7514 ded1d380 c071c6e0 00000004 c07105d8
[   24.192119] 1ea0: 01e2a738 c047f1e0 c0600cc0 df481ec4 00000003 00000000 00000003 c05c74d8
[   24.200278] 1ec0: ded1d380 c071c6e0 c05c7514 c07105d8 01e2a738 c0069444 c06d905c 00000003
[   24.208438] 1ee0: 00000003 ded1d380 c06d9064 00000004 c05c3fc0 c0067d4c df535ab0 ded1d380
[   24.216596] 1f00: df481f80 ded1d380 00000004 ded1d1cc ded1d1c0 c0221724 00000004 c016ca6c
[   24.224756] 1f20: c016ca28 00000000 00000000 c016c1d4 00000000 00000000 b6f37000 df481f80
[   24.232915] 1f40: decedd80 00000004 df480000 df480000 b6f37000 c0110920 df47839c 60000013
[   24.241074] 1f60: 00000000 00000000 decedd80 decedd80 00000004 df480000 b6f37000 c0110da8
[   24.249233] 1f80: 00000000 00000000 00000004 b6edf5d8 00000004 b6f37000 00000004 c000f2a8
[   24.257393] 1fa0: 00001000 c000f0e0 b6edf5d8 00000004 00000001 b6f37000 00000004 00000000
[   24.265551] 1fc0: b6edf5d8 00000004 b6f37000 00000004 00000004 00000001 00000000 01e2a738
[   24.273711] 1fe0: 00000000 beba0a20 b6e1f4f0 b6e7022c 60000010 00000001 ffffffff ffffffff
[   24.281885] [<c048516c>] (mutex_lock) from [<c02a14b4>] (drm_modeset_lock_all+0x30/0xbc)
[   24.289950] [<c02a14b4>] (drm_modeset_lock_all) from [<c02aec7c>] (exynos_drm_suspend+0xc/0x64)
[   24.298627] [<c02aec7c>] (exynos_drm_suspend) from [<c02aecf4>] (exynos_drm_sys_suspend+0x20/0x34)
[   24.307568] [<c02aecf4>] (exynos_drm_sys_suspend) from [<c02c2010>] (platform_pm_suspend+0x2c/0x54)
[   24.316597] [<c02c2010>] (platform_pm_suspend) from [<c02c9470>] (dpm_run_callback+0x48/0x170)
[   24.325188] [<c02c9470>] (dpm_run_callback) from [<c02ca660>] (__device_suspend+0x128/0x39c)
[   24.333606] [<c02ca660>] (__device_suspend) from [<c02cbe18>] (dpm_suspend+0x5c/0x314)
[   24.341506] [<c02cbe18>] (dpm_suspend) from [<c0068a74>] (suspend_devices_and_enter+0x8c/0x598)
[   24.350185] [<c0068a74>] (suspend_devices_and_enter) from [<c0069444>] (pm_suspend+0x4c4/0x5d0)
[   24.358862] [<c0069444>] (pm_suspend) from [<c0067d4c>] (state_store+0x70/0xd4)
[   24.366156] [<c0067d4c>] (state_store) from [<c0221724>] (kobj_attr_store+0x14/0x20)
[   24.373885] [<c0221724>] (kobj_attr_store) from [<c016ca6c>] (sysfs_kf_write+0x44/0x48)
[   24.381867] [<c016ca6c>] (sysfs_kf_write) from [<c016c1d4>] (kernfs_fop_write+0xc0/0x17c)
[   24.390027] [<c016c1d4>] (kernfs_fop_write) from [<c0110920>] (vfs_write+0xa0/0x1c4)
[   24.397750] [<c0110920>] (vfs_write) from [<c0110da8>] (SyS_write+0x40/0x8c)
[   24.404782] [<c0110da8>] (SyS_write) from [<c000f0e0>] (ret_fast_syscall+0x0/0x3c)
[   24.412332] Code: e92d4010 e1a04000 f57ff05b f590f000 (e1903f9f)
[   24.418448] ---[ end trace cfa06690eabe8dd5 ]---
[   24.423032] Kernel panic - not syncing: Fatal exception
[   24.428220] CPU1: stopping
[   24.430905] CPU: 1 PID: 0 Comm: swapper/1 Tainted: G      D       3.16.0-rc3-00035-geba20bbdde04-dirty #51
[   24.440549] [<c0016440>] (unwind_backtrace) from [<c001294c>] (show_stack+0x10/0x14)
[   24.448269] [<c001294c>] (show_stack) from [<c04811e8>] (dump_stack+0x80/0xcc)
[   24.455472] [<c04811e8>] (dump_stack) from [<c001495c>] (handle_IPI+0x130/0x15c)
[   24.462850] [<c001495c>] (handle_IPI) from [<c000862c>] (gic_handle_irq+0x60/0x68)
[   24.470400] [<c000862c>] (gic_handle_irq) from [<c0013440>] (__irq_svc+0x40/0x70)
[   24.477860] Exception stack(0xdf4bdf88 to 0xdf4bdfd0)
[   24.482898] df80:                   ffffffed 00000000 00000000 00000000 df4bc000 c06d042c
[   24.491058] dfa0: 00000000 ffffffed c06d03c0 00000000 c070c288 00000000 00000000 df4bdfd0
[   24.499214] dfc0: c0010324 c0010328 60000013 ffffffff
[   24.504254] [<c0013440>] (__irq_svc) from [<c0010328>] (arch_cpu_idle+0x28/0x30)
[   24.511634] [<c0010328>] (arch_cpu_idle) from [<c005f110>] (cpu_startup_entry+0x2c4/0x3f0)
[   24.519878] [<c005f110>] (cpu_startup_entry) from [<400086c4>] (0x400086c4)
[   24.526821] ---[ end Kernel panic - not syncing: Fatal exception
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>