ext4: release bs.bh before re-using in ext4_xattr_block_find()

bs.bh was taken in previous ext4_xattr_block_find() call,
it should be released before re-using

Fixes: 7e01c8e5 ("ext3/4: fix uninitialized bs in ...")
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org # 2.6.26