drm/omap: drm_atomic_get_plane_state() may return ERR_PTR

drm_atomic_get_plane_state() may return ERR_PTR. Handle
drm_atomic_get_plane_state() return values right in
omap_crtc_atomic_set_property().

Signed-off-by: Jyri Sarha <jsarha@ti.com>
Acked-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

drivers/gpu/drm/omapdrm/omap_crtc.c

@@ -433,8 +433,8 @@ static int omap_crtc_atomic_set_property(struct drm_crtc *crtc,
 	 */
 
 	plane_state = drm_atomic_get_plane_state(state->state, plane);
-	if (!plane_state)
-		return -EINVAL;
+	if (IS_ERR(plane_state))
+		return PTR_ERR(plane_state);
 
 	return drm_atomic_plane_set_property(plane, plane_state, property, val);
 }