UBI: fix memory leak in update path

When truncating an UBI volume, UBI should allocates a PEB-sized
buffer but does not release it, which leads to memory leaks.
This patch fixes the issue.

Reported-by: Marek Skuczynski <mareksk7@gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Tested-by: Marek Skuczynski <mareksk7@gmail.com>
Cc: stable@kernel.org
diff --git a/drivers/mtd/ubi/upd.c b/drivers/mtd/ubi/upd.c
index c1d7b88..425bf5a 100644
--- a/drivers/mtd/ubi/upd.c
+++ b/drivers/mtd/ubi/upd.c
@@ -155,6 +155,7 @@
 		if (err)
 			return err;
 		vol->updating = 0;
+		return 0;
 	}
 
 	vol->upd_buf = vmalloc(ubi->leb_size);