UBI: rename_volumes: Use UBI_METAONLY

By using UBI_METAONLY in rename_volumes() it is now possible to rename
an UBI volume atomically while it is open for writing.
This is useful for firmware upgrades.

Cc: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Cc: Andrew Murray <amurray@embedded-bits.co.uk>
Signed-off-by: NRichard Weinberger <richard@nod.at>
Tested-by: NGuido Martínez <guido@vanguardiasur.com.ar>
Reviewed-by: NGuido Martínez <guido@vanguardiasur.com.ar>
Tested-by: NChristoph Fritz <chf.fritz@googlemail.com>
Tested-by: NAndrew Murray <amurray@embedded-bits.co.uk>

drivers/mtd/ubi/cdev.c

@@ -736,7 +736,7 @@ static int rename_volumes(struct ubi_device *ubi,
 			goto out_free;
 		}
 
-		re->desc = ubi_open_volume(ubi->ubi_num, vol_id, UBI_READWRITE);
+		re->desc = ubi_open_volume(ubi->ubi_num, vol_id, UBI_METAONLY);
 		if (IS_ERR(re->desc)) {
 			err = PTR_ERR(re->desc);
 			ubi_err(ubi, "cannot open volume %d, error %d",