media: mediatek: vcodec: prevent kernel crash when rmmod mtk-vcodec-dec.ko

media: mediatek: vcodec: prevent kernel crash when rmmod mtk-vcodec-dec.ko

If the driver support subdev mode, the parameter "dev->pm.dev" will be
NULL in mtk_vcodec_dec_remove. Kernel will crash when try to rmmod
mtk-vcodec-dec.ko.

[ 4380.702726] pc : do_raw_spin_trylock+0x4/0x80
[ 4380.707075] lr : _raw_spin_lock_irq+0x90/0x14c
[ 4380.711509] sp : ffff80000819bc10
[ 4380.714811] x29: ffff80000819bc10 x28: ffff3600c03e4000 x27: 0000000000000000
[ 4380.721934] x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000
[ 4380.729057] x23: ffff3600c0f34930 x22: ffffd5e923549000 x21: 0000000000000220
[ 4380.736179] x20: 0000000000000208 x19: ffffd5e9213e8ebc x18: 0000000000000020
[ 4380.743298] x17: 0000002000000000 x16: ffffd5e9213e8e90 x15: 696c346f65646976
[ 4380.750420] x14: 0000000000000000 x13: 0000000000000001 x12: 0000000000000040
[ 4380.757542] x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000
[ 4380.764664] x8 : 0000000000000000 x7 : ffff3600c7273ae8 x6 : ffffd5e9213e8ebc
[ 4380.771786] x5 : 0000000000000000 x4 : 0000000000000001 x3 : 0000000000000000
[ 4380.778908] x2 : 0000000000000000 x1 : ffff3600c03e4000 x0 : 0000000000000208
[ 4380.786031] Call trace:
[ 4380.788465]  do_raw_spin_trylock+0x4/0x80
[ 4380.792462]  __pm_runtime_disable+0x2c/0x1b0
[ 4380.796723]  mtk_vcodec_dec_remove+0x5c/0xa0 [mtk_vcodec_dec]
[ 4380.802466]  platform_remove+0x2c/0x60
[ 4380.806204]  __device_release_driver+0x194/0x250
[ 4380.810810]  driver_detach+0xc8/0x15c
[ 4380.814462]  bus_remove_driver+0x5c/0xb0
[ 4380.818375]  driver_unregister+0x34/0x64
[ 4380.822288]  platform_driver_unregister+0x18/0x24
[ 4380.826979]  mtk_vcodec_dec_driver_exit+0x1c/0x888 [mtk_vcodec_dec]
[ 4380.833240]  __arm64_sys_delete_module+0x190/0x224
[ 4380.838020]  invoke_syscall+0x48/0x114
[ 4380.841760]  el0_svc_common.constprop.0+0x60/0x11c
[ 4380.846540]  do_el0_svc+0x28/0x90
[ 4380.849844]  el0_svc+0x4c/0x100
[ 4380.852975]  el0t_64_sync_handler+0xec/0xf0
[ 4380.857148]  el0t_64_sync+0x190/0x194
[ 4380.860801] Code: 94431515 17ffffca d503201f d503245f (b9400004)

Signed-off-by: Yunfei Dong <yunfei.dong@mediatek.com>
Tested-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>