ocfs2: Fix NULL pointer deref when writing local dquot

commit_dqblk() can write quota info to global file. That is actually a bad
thing to do because if we are just modifying local quota file, we are not
prepared (do not hold proper locks, do not have transaction credits) to do
a modification of the global quota file. So do not use commit_dqblk() and
instead call our writing function directly.

Acked-by: Joel Becker <Joel.Becker@oracle.com>
Signed-off-by: Jan Kara <jack@suse.cz>