ocfs2/dlm: return zero if deref_done message is successfully handled

dlm_deref_lockres_done_handler() should return zero if the message is
successfully handled.

Fixes: 60d663cb ("ocfs2/dlm: add DEREF_DONE message").
Signed-off-by: xuejiufei <xuejiufei@huawei.com>
Reviewed-by: Joseph Qi <joseph.qi@huawei.com>
Cc: Mark Fasheh <mfasheh@suse.de>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ocfs2/dlm/dlmmaster.c

@@ -2455,6 +2455,8 @@ int dlm_deref_lockres_done_handler(struct o2net_msg *msg, u32 len, void *data,
 
 	spin_unlock(&dlm->spinlock);
 
+	ret = 0;
+
 done:
 	dlm_put(dlm);
 	return ret;