commit 281fda27 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>
[ luis: backported to 3.16:
  - no ubi_device parameter for the ubi_err() macro in 3.16 ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>