UBI: fix gcc warning

Fix the following warning:

drivers/mtd/ubi/vmt.c: In function 'ubi_rename_volumes':
drivers/mtd/ubi/vmt.c:642: warning: statement with no effect

Signed-off-by: Artem Bityutskiy <[e-mail]>

drivers/mtd/ubi/vmt.c

···
 	}
 
 	if (!err)
-		paranoid_check_volumes(ubi);
+		err = paranoid_check_volumes(ubi);
 	return err;
 }