drm/amd/display: Fix null pointer deref in dcn20_resource.c

In the Linux kernel, the following vulnerability has been resolved:

drm/amd/display: Fix null pointer deref in dcn20_resource.c

Fixes a hang thats triggered when MPV is run on a DCN401 dGPU:

mpv --hwdec=vaapi --vo=gpu --hwdec-codecs=all

and then enabling fullscreen playback (double click on the video)

The following calltrace will be seen:

[ 181.843989] BUG: kernel NULL pointer dereference, address: 0000000000000000
[ 181.843997] #PF: supervisor instruction fetch in kernel mode
[ 181.844003] #PF: error_code(0x0010) - not-present page
[ 181.844009] PGD 0 P4D 0
[ 181.844020] Oops: 0010 [#1] PREEMPT SMP NOPTI
[ 181.844028] CPU: 6 PID: 1892 Comm: gnome-shell Tainted: G W OE 6.5.0-41-generic #41~22.04.2-Ubuntu
[ 181.844038] Hardware name: System manufacturer System Product Name/CROSSHAIR VI HERO, BIOS 6302 10/23/2018
[ 181.844044] RIP: 0010:0x0
[ 181.844079] Code: Unable to access opcode bytes at 0xffffffffffffffd6.
[ 181.844084] RSP: 0018:ffffb593c2b8f7b0 EFLAGS: 00010246
[ 181.844093] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000004
[ 181.844099] RDX: ffffb593c2b8f804 RSI: ffffb593c2b8f7e0 RDI: ffff9e3c8e758400
[ 181.844105] RBP: ffffb593c2b8f7b8 R08: ffffb593c2b8f9c8 R09: ffffb593c2b8f96c
[ 181.844110] R10: 0000000000000000 R11: 0000000000000000 R12: ffffb593c2b8f9c8
[ 181.844115] R13: 0000000000000001 R14: ffff9e3c88000000 R15: 0000000000000005
[ 181.844121] FS: 00007c6e323bb5c0(0000) GS:ffff9e3f85f80000(0000) knlGS:0000000000000000
[ 181.844128] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 181.844134] CR2: ffffffffffffffd6 CR3: 0000000140fbe000 CR4: 00000000003506e0
[ 181.844141] Call Trace:
[ 181.844146] <TASK>
[ 181.844153] ? show_regs+0x6d/0x80
[ 181.844167] ? __die+0x24/0x80
[ 181.844179] ? page_fault_oops+0x99/0x1b0
[ 181.844192] ? do_user_addr_fault+0x31d/0x6b0
[ 181.844204] ? exc_page_fault+0x83/0x1b0
[ 181.844216] ? asm_exc_page_fault+0x27/0x30
[ 181.844237] dcn20_get_dcc_compression_cap+0x23/0x30 [amdgpu]
[ 181.845115] amdgpu_dm_plane_validate_dcc.constprop.0+0xe5/0x180 [amdgpu]
[ 181.845985] amdgpu_dm_plane_fill_plane_buffer_attributes+0x300/0x580 [amdgpu]
[ 181.846848] fill_dc_plane_info_and_addr+0x258/0x350 [amdgpu]
[ 181.847734] fill_dc_plane_attributes+0x162/0x350 [amdgpu]
[ 181.848748] dm_update_plane_state.constprop.0+0x4e3/0x6b0 [amdgpu]
[ 181.849791] ? dm_update_plane_state.constprop.0+0x4e3/0x6b0 [amdgpu]
[ 181.850840] amdgpu_dm_atomic_check+0xdfe/0x1760 [amdgpu]