usb/chipidea: fix oops on memory allocation failure

When CMA fails to initialize in v3.12-rc4, the chipidea driver oopses
the kernel while trying to remove and put the HCD which doesn't exist:

WARNING: CPU: 0 PID: 6 at /home/rmk/git/linux-rmk/arch/arm/mm/dma-mapping.c:511
__dma_alloc+0x200/0x240()
coherent pool not initialised!
Modules linked in:
CPU: 0 PID: 6 Comm: kworker/u2:0 Tainted: G        W    3.12.0-rc4+ #56
Workqueue: deferwq deferred_probe_work_func
Backtrace:
[<c001218c>] (dump_backtrace+0x0/0x10c) from [<c0012328>] (show_stack+0x18/0x1c)
 r6:c05fd9cc r5:000001ff r4:00000000 r3:df86ad00
[<c0012310>] (show_stack+0x0/0x1c) from [<c05f3a4c>] (dump_stack+0x70/0x8c)
[<c05f39dc>] (dump_stack+0x0/0x8c) from [<c00230a8>] (warn_slowpath_common+0x6c/0x8c)
 r4:df883a60 r3:df86ad00
[<c002303c>] (warn_slowpath_common+0x0/0x8c) from [<c002316c>] (warn_slowpath_fmt+0x38/0x40)
 r8:ffffffff r7:00001000 r6:c083b808 r5:00000000 r4:df2efe80
[<c0023134>] (warn_slowpath_fmt+0x0/0x40) from [<c00196bc>] (__dma_alloc+0x200/0x240)
 r3:00000000 r2:c05fda00
[<c00194bc>] (__dma_alloc+0x0/0x240) from [<c001982c>] (arm_dma_alloc+0x88/0xa0)
[<c00197a4>] (arm_dma_alloc+0x0/0xa0) from [<c03e2904>] (ehci_setup+0x1f4/0x438)
[<c03e2710>] (ehci_setup+0x0/0x438) from [<c03cbd60>] (usb_add_hcd+0x18c/0x664)
[<c03cbbd4>] (usb_add_hcd+0x0/0x664) from [<c03e89f4>] (host_start+0xf0/0x180)
[<c03e8904>] (host_start+0x0/0x180) from [<c03e7c34>] (ci_hdrc_probe+0x360/0x670
)
 r6:df2ef410 r5:00000000 r4:df2c3010 r3:c03e8904
[<c03e78d4>] (ci_hdrc_probe+0x0/0x670) from [<c0311044>] (platform_drv_probe+0x20/0x24)
[<c0311024>] (platform_drv_probe+0x0/0x24) from [<c030fcac>] (driver_probe_device+0x9c/0x234)
...
---[ end trace c88ccaf3969e8422 ]---
Unable to handle kernel NULL pointer dereference at virtual address 00000028
pgd = c0004000
[00000028] *pgd=00000000
Internal error: Oops: 17 [#1] SMP ARM
Modules linked in:
CPU: 0 PID: 6 Comm: kworker/u2:0 Tainted: G        W    3.12.0-rc4+ #56
Workqueue: deferwq deferred_probe_work_func
task: df86ad00 ti: df882000 task.ti: df882000
PC is at usb_remove_hcd+0x10/0x150
LR is at host_stop+0x1c/0x3c
pc : [<c03cacec>]    lr : [<c03e88e4>]    psr: 60000013
sp : df883b50  ip : df883b78  fp : df883b74
r10: c11f4c54  r9 : c0836450  r8 : df30c400
r7 : fffffff4  r6 : df2ef410  r5 : 00000000  r4 : df2c3010
r3 : 00000000  r2 : 00000000  r1 : df86b0a0  r0 : 00000000
Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment kernel
Control: 10c53c7d  Table: 2f29404a  DAC: 00000015
Process kworker/u2:0 (pid: 6, stack limit = 0xdf882240)
Stack: (0xdf883b50 to 0xdf884000)
...
Backtrace:
[<c03cacdc>] (usb_remove_hcd+0x0/0x150) from [<c03e88e4>] (host_stop+0x1c/0x3c)
 r6:df2ef410 r5:00000000 r4:df2c3010
[<c03e88c8>] (host_stop+0x0/0x3c) from [<c03e8aa0>] (ci_hdrc_host_destroy+0x1c/0x20)
 r5:00000000 r4:df2c3010
[<c03e8a84>] (ci_hdrc_host_destroy+0x0/0x20) from [<c03e7c80>] (ci_hdrc_probe+0x3ac/0x670)
[<c03e78d4>] (ci_hdrc_probe+0x0/0x670) from [<c0311044>] (platform_drv_probe+0x20/0x24)
[<c0311024>] (platform_drv_probe+0x0/0x24) from [<c030fcac>] (driver_probe_device+0x9c/0x234)
[<c030fc10>] (driver_probe_device+0x0/0x234) from [<c030ff28>] (__device_attach+0x44/0x48)
...
---[ end trace c88ccaf3969e8423 ]---

Fix this so at least we can continue booting and get to a shell prompt.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Tested-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/chipidea/host.c

@@ -100,8 +100,10 @@ static void host_stop(struct ci_hdrc *ci)
 {
 	struct usb_hcd *hcd = ci->hcd;
 
+	if (hcd) {
 		usb_remove_hcd(hcd);
 		usb_put_hcd(hcd);
+	}
 	if (ci->platdata->reg_vbus)
 		regulator_disable(ci->platdata->reg_vbus);
 }