udl: handle EDID failure properly.

Don't oops seems proper.

Cc: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/udl/udl_connector.c

@@ -61,6 +61,10 @@ static int udl_get_modes(struct drm_connector *connector)
 	int ret;
 
 	edid = (struct edid *)udl_get_edid(udl);
+	if (!edid) {
+		drm_mode_connector_update_edid_property(connector, NULL);
+		return 0;
+	}
 
 	/*
 	 * We only read the main block, but if the monitor reports extension