UBI: Validate data_size

commit 281fda27673f833a01d516658a64d22a32c8e072 upstream.

Make sure that data_size is less than LEB size.
Otherwise a handcrafted UBI image is able to trigger
an out of bounds memory access in ubi_compare_lebs().

Signed-off-by: Richard Weinberger <richard@nod.at>
Reviewed-by: David Gstir <david@sigma-star.at>
[bwh: Backported to 3.2: drop first argument to ubi_err()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --cc drivers/mtd/ubi/io.c
Simple merge