blk-mq: mq plug list breakage

We switched to plug mq_list for mq, but some code are still using old list.

Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk-core.c b/block/blk-core.c
index 9677c65..936876a 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1401,13 +1401,19 @@
 	struct blk_plug *plug;
 	struct request *rq;
 	bool ret = false;
+	struct list_head *plug_list;
 
 	plug = current->plug;
 	if (!plug)
 		goto out;
 	*request_count = 0;
 
-	list_for_each_entry_reverse(rq, &plug->list, queuelist) {
+	if (q->mq_ops)
+		plug_list = &plug->mq_list;
+	else
+		plug_list = &plug->list;
+
+	list_for_each_entry_reverse(rq, plug_list, queuelist) {
 		int el_ret;
 
 		if (rq->q == q)