drm/amd/display: fix dereference before NULL check

The "plane_state" pointer was access before checking if it was NULL.

Avoid a possible NULL pointer dereference by accessing the plane
address after the check.

Addresses-Coverity-ID: 1493892 ("Dereference before null check")
Fixes: 3f68c01 ("drm/amd/display: add cyan_skillfish display support")
Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn201/dcn201_hwseq.c

@@ -134,11 +134,12 @@ void dcn201_update_plane_addr(const struct dc *dc, struct pipe_ctx *pipe_ctx)
 	PHYSICAL_ADDRESS_LOC addr;
 	struct dc_plane_state *plane_state = pipe_ctx->plane_state;
 	struct dce_hwseq *hws = dc->hwseq;
-	struct dc_plane_address uma = plane_state->address;
+	struct dc_plane_address uma;
 
 	if (plane_state == NULL)
 		return;
 
+	uma = plane_state->address;
 	addr_patched = patch_address_for_sbs_tb_stereo(pipe_ctx, &addr);
 
 	plane_address_in_gpu_space_to_uma(hws, &uma);