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

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CVE-2024-43899

CVE-2024-43899 affects the Linux kernel’s DRM AMD display path. The vulnerability is a NULL pointer dereference in dcn20_resource.c that can cause a hang when MPV runs on a DCN401 dGPU, specifically during fullscreen playback after enabling fullscreen (double click). Affected component/function c...