drm/mediatek: Check return value of mtk_drm_ddp_comp_for_plane.

The mtk_drm_ddp_comp_for_plane can return NULL, but the usage doesn't
check for it. Add check for it.

Fixes: d6b53f6835 ("drm/mediatek: Add helper to get component for a plane")
Signed-off-by: Pi-Hsun Shih <pihsun@chromium.org>
Signed-off-by: CK Hu <ck.hu@mediatek.com>

drivers/gpu/drm/mediatek/mtk_drm_crtc.c

@@ -310,7 +310,9 @@ static int mtk_crtc_ddp_hw_init(struct mtk_drm_crtc *mtk_crtc)
 
 		plane_state = to_mtk_plane_state(plane->state);
 		comp = mtk_drm_ddp_comp_for_plane(crtc, plane, &local_layer);
-		mtk_ddp_comp_layer_config(comp, local_layer, plane_state);
+		if (comp)
+			mtk_ddp_comp_layer_config(comp, local_layer,
+						  plane_state);
 	}
 
 	return 0;
@@ -386,8 +388,9 @@ static void mtk_crtc_ddp_config(struct drm_crtc *crtc)
 			comp = mtk_drm_ddp_comp_for_plane(crtc, plane,
 							  &local_layer);
 
-			mtk_ddp_comp_layer_config(comp, local_layer,
-						  plane_state);
+			if (comp)
+				mtk_ddp_comp_layer_config(comp, local_layer,
+							  plane_state);
 			plane_state->pending.config = false;
 		}
 		mtk_crtc->pending_planes = false;
@@ -401,7 +404,9 @@ int mtk_drm_crtc_plane_check(struct drm_crtc *crtc, struct drm_plane *plane,
 	struct mtk_ddp_comp *comp;
 
 	comp = mtk_drm_ddp_comp_for_plane(crtc, plane, &local_layer);
-	return mtk_ddp_comp_layer_check(comp, local_layer, state);
+	if (comp)
+		return mtk_ddp_comp_layer_check(comp, local_layer, state);
+	return 0;
 }
 
 static void mtk_drm_crtc_atomic_enable(struct drm_crtc *crtc,