drm: fsl-dcu: Fix no fb check bug

For state->fb or state->crtc may be NULL in fsl_dcu_drm_plane_atomic_check
function, if so, return 0.
Signed-off-by: Meng Yi <meng.yi@nxp.com>
Signed-off-by: Jianwei Wang <jianwei.wang.chn@gmail.com>
Signed-off-by: Stefan Agner <stefan@agner.ch>

drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_plane.c

@@ -41,6 +41,9 @@ static int fsl_dcu_drm_plane_atomic_check(struct drm_plane *plane,
 {
 	struct drm_framebuffer *fb = state->fb;
 
+	if (!state->fb || !state->crtc)
+		return 0;
+
 	switch (fb->pixel_format) {
 	case DRM_FORMAT_RGB565:
 	case DRM_FORMAT_RGB888: