Below crash observed with commit 7acc6197
(usb: musb: Idle path retention and offmode support for OMAP3)
during board reboot.

The musb clock was disabled when musb_shutdown() was called by
platform_drv_shutdown in which there are register accesses.
call pm_runtime_get_sync() and pm_runtime_put_sync() in the
musb_shutdown function.

/ # [  172.368774] Unhandled fault: imprecise external abort (0x1406) at 0x400f0000
[  172.376190] Internal error: : 1406 [#1] SMP
[  172.380554] last sysfs file: /sys/devices/platform/omap/omap_i2c.4/i2c-4/i2c-dev/i2c-4/dev
[  172.389221] Modules linked in:
[  172.392456] CPU: 0    Tainted: G        W    (2.6.38-06671-geddecbb6 #33)
[  172.399475] PC is at do_raw_spin_unlock+0x50/0xc0
[  172.404418] LR is at _raw_spin_unlock_irqrestore+0x24/0x44
[  172.410186] pc : [<c069bfdc>]    lr : [<c085a7f8>]    psr: 60000093
[  172.410186] sp : ee993e40  ip : c0d00240  fp : bea9cf14
[  172.422241] r10: 00000000  r9 : ee992000  r8 : c04b2fa8
[  172.427703] r7 : 00000000  r6 : c0fa46c0  r5 : ef966124  r4 : ef966124
[  172.434539] r3 : ef92cbc0  r2 : ef92cbc0  r1 : 00000000  r0 : ef966124
[  172.441406] Flags: nZCv  IRQs off  FIQs on  Mode SVC_32  ISA ARM  Segment user
[  172.448974] Control: 10c5387d  Table: ae8d804a  DAC: 00000015
[  172.454986] Process init (pid: 1094, stack limit = 0xee9922f8)
[  172.461120] Stack: (0xee993e40 to 0xee994000)
[  172.465667] 3e40: a0000013 c085a7f8 ef966124 a0000013 c0fa46c0 c0761ab4 c0761a70 ef95c008
[  172.474273] 3e60: ef95c014 c06e2fd0 c06e2fbc c06dea90 00000000 01234567 28121969 c04fccb4
[  172.482849] 3e80: 00000000 c04fcd04 c0a302bc c04fce44 c0a02600 00000001 00000000 c085cd04
[  172.491424] 3ea0: 00000000 00000002 c09ea000 c085afc0 ee993f24 00000000 00040001 00000445
[  172.499999] 3ec0: a8eb9d34 00000027 00000000 00000000 00000000 c0a56a4c 00000000 00000000
[  172.508575] 3ee0: 00000002 60000093 00000000 c0519aac 00000002 00000080 00000000 c0550420
[  172.517150] 3f00: 00000000 00000002 ee970000 c0a56a3c c0a56a20 00000002 c0a56a3c 00000000
[  172.525726] 3f20: c0a56a3c 0000000a c1580e00 c0a56a20 00000002 c0a56a3c c1580e00 c0a56a20
[  172.534301] 3f40: ef92cbc0 c05173a0 00000001 ef92cbc0 c0576190 c04e3174 20000013 c0517324
[  172.542877] 3f60: ef815c00 ee90b720 c04e3174 c0576190 00000001 ef92cbc0 c04b2f00 ffffffff
[  172.551483] 3f80: 00000058 c0517324 00000000 00000000 ffffffff 00000000 00000000 ffffffff
[  172.560058] 3fa0: 00000058 c04b2de0 00000000 00000000 fee1dead 28121969 01234567 00000000
[  172.568634] 3fc0: 00000000 00000000 ffffffff 00000058 00000000 00000001 400aa000 bea9cf14
[  172.577209] 3fe0: 000ea148 bea9c958 000aa750 40225728 60000010 fee1dead 00000000 00000000
[  172.585784] [<c069bfdc>] (do_raw_spin_unlock+0x50/0xc0) from [<c085a7f8>] (_raw_spin_unlock_irqrestore+0x24/0x44)
[  172.596588] [<c085a7f8>] (_raw_spin_unlock_irqrestore+0x24/0x44) from [<c0761ab4>] (musb_shutdown+0x44/0x88)
[  172.606933] [<c0761ab4>] (musb_shutdown+0x44/0x88) from [<c06e2fd0>] (platform_drv_shutdown+0x14/0x18)
[  172.616699] [<c06e2fd0>] (platform_drv_shutdown+0x14/0x18) from [<c06dea90>] (device_shutdown+0x74/0xb4)
[  172.626647] [<c06dea90>] (device_shutdown+0x74/0xb4) from [<c04fccb4>] (kernel_restart_prepare+0x24/0x38)
[  172.636688] [<c04fccb4>] (kernel_restart_prepare+0x24/0x38) from [<c04fcd04>] (kernel_restart+0xc/0x48)
[  172.646545] [<c04fcd04>] (kernel_restart+0xc/0x48) from [<c04fce44>] (sys_reboot+0xfc/0x1d8)
[  172.655426] [<c04fce44>] (sys_reboot+0xfc/0x1d8) from [<c04b2de0>] (ret_fast_syscall+0x0/0x3c)
[  172.664459] Code: e3c3303f e594200c e593300c e1520003 (0a000002)
[  172.670867] ------------[ cut here ]------------
Signed-off-by: Hema HK <hemahk@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>