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

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]

Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>