UBI: use separate mutex for volumes checking

Introduce a separate mutex which serializes volumes checking,
because we cammot really use volumes_mutex - it cases reverse
locking problems with mtd_tbl_mutex when gluebi is used -
thanks to lockdep.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

drivers/mtd/ubi/build.c

@@ -703,6 +703,7 @@ int ubi_attach_mtd_dev(struct mtd_info *mtd, int ubi_num, int vid_hdr_offset)
 		goto out_free;
 
 	mutex_init(&ubi->buf_mutex);
+	mutex_init(&ubi->ckvol_mutex);
 	ubi->peb_buf1 = vmalloc(ubi->peb_size);
 	if (!ubi->peb_buf1)
 		goto out_free;