drm/amd/display: Fix potential nullptr error

[Why]
Fix surface/plane potential nullptr

[How]
add null check

Signed-off-by: Bhawanpreet Lakha <[e-mail]>
Reviewed-by: Aric Cyr <[e-mail]>
Acked-by: Leo Li <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

···
 	struct dc_stream_update stream_update;
 	enum surface_update_type update_type = UPDATE_TYPE_FAST;
 
+	if (!updates || !surface) {
+		DRM_ERROR("Plane or surface update failed to allocate");
+		/* Set type to FULL to avoid crashing in DC*/
+		update_type = UPDATE_TYPE_FULL;
+		goto ret;
+	}
 
 	for_each_oldnew_crtc_in_state(state, crtc, old_crtc_state, new_crtc_state, i) {
 		new_dm_crtc_state = to_dm_crtc_state(new_crtc_state);