xen/blkfront: avoid compiler warning from missing cases

Fix:
drivers/block/xen-blkfront.c: In function ‘blkfront_connect’:
drivers/block/xen-blkfront.c:933: warning: enumeration value ‘BLKIF_STATE_DISCONNECTED’ not handled in switch
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

drivers/block/xen-blkfront.c

@@ -947,6 +947,9 @@ static void blkfront_connect(struct blkfront_info *info)
 		/* fall through */
 	case BLKIF_STATE_SUSPENDED:
 		return;
+
+	default:
+		break;
 	}
 
 	dev_dbg(&info->xbdev->dev, "%s:%s.\n",