ext4: add missing brelse() update_backups()'s error path

commit ea0abbb6 upstream.

Fixes: ac27a0ec ("ext4: initial copy of files from ext3")
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org # 2.6.19
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>