drm/amd/display: Add null check for pipe_ctx->plane_state in dcn20_program_pipe

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: drm/amd/display: Add null check for pipe_ctx->plane_state in dcn20_program_pipe This commit addresses a null pointer dereference issue in the `dcn20_program_pipe` function. The issue could occur when `pipe_ctx->plane_state` is null. The fix adds a check to ensure `pipe_ctx->plane_state` is not null before accessing. This prevents a null pointer dereference. Reported by smatch: drivers/gpu/drm/amd/amdgpu/../display/dc/hwss/dcn20/dcn20_hwseq.c:1925 dcn20_program_pipe() error: we previously assumed 'pipe_ctx->plane_state' could be null (see line 1877)

References

• https://git.kernel.org/stable/c/68f75e6f08aad66069a629db8d7840919156c761
• https://git.kernel.org/stable/c/65a6fee22d5cfa645cb05489892dc9cd3d142fc2
• https://git.kernel.org/stable/c/8e4ed3cf1642df0c4456443d865cff61a9598aa8