ubi: Fix out of bounds write in volume update code

ubi: Fix out of bounds write in volume update code

Orabug: 23330992

[ Upstream commit e4f6daac20332448529b11f09388f1d55ef2084c ]

ubi_start_leb_change() allocates too few bytes.
ubi_more_leb_change_data() will write up to req->upd_bytes +
ubi->min_io_size bytes.

Cc: stable@vger.kernel.org
Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
(cherry picked from commit 325940deb74b23351f507d5f1e1e01592c1efa1c)

Signed-off-by: Dan Duval <dan.duval@oracle.com>