UBIFS: allow more than one volume to be mounted

UBIFS uses a bdi device per volume, but does not care to hand out unique
names to each of them. This causes an error when trying to mount more
than one volumes. Append the UBI volume and device ID to avoid that.

[Amended a bit by Artem Bityutskiy]

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Cc: Artem Bityutskiy <dedekind@infradead.org>
Cc: Adrian Hunter <ext-adrian.hunter@nokia.com>
Cc: linux-mtd@lists.infradead.org
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/fs/ubifs/super.c b/fs/ubifs/super.c
index 3507d0e..26d2e0d 100644
--- a/fs/ubifs/super.c
+++ b/fs/ubifs/super.c
@@ -1976,7 +1976,8 @@
 	err  = bdi_init(&c->bdi);
 	if (err)
 		goto out_close;
-	err = bdi_register(&c->bdi, NULL, "ubifs");
+	err = bdi_register(&c->bdi, NULL, "ubifs_%d_%d",
+			   c->vi.ubi_num, c->vi.vol_id);
 	if (err)
 		goto out_bdi;