ext4: avoid buffer leak on shutdown in ext4_mark_iloc_dirty()

ext4_mark_iloc_dirty() callers expect that it releases iloc->bh
even if it returns an error.

Fixes: 0db1ff22 ("ext4: add shutdown bit and check for it")
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org # 4.11