imx-drm: imx-ldb: Check 'mode' pointer first

Fix the following static checker warning:

drivers/staging/imx-drm/imx-ldb.c:109 imx_ldb_connector_get_modes() error: potential null dereference 'mode'.  (drm_mode_create returns null)
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NFabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/imx-drm/imx-ldb.c

@@ -106,6 +106,8 @@ static int imx_ldb_connector_get_modes(struct drm_connector *connector)
 		struct drm_display_mode *mode;
 
 		mode = drm_mode_create(connector->dev);
+		if (!mode)
+			return -EINVAL;
 		drm_mode_copy(mode, &imx_ldb_ch->mode);
 		mode->type |= DRM_MODE_TYPE_DRIVER | DRM_MODE_TYPE_PREFERRED;
 		drm_mode_probed_add(connector, mode);