nvme: Fix a race condition related to stopping queues

Avoid that nvme_queue_rq() is still running when nvme_stop_queues()
returns.
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Keith Busch <keith.busch@intel.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/nvme/host/core.c

@@ -2081,7 +2081,7 @@ void nvme_stop_queues(struct nvme_ctrl *ctrl)
 		queue_flag_set(QUEUE_FLAG_STOPPED, ns->queue);
 		spin_unlock_irq(ns->queue->queue_lock);
 
-		blk_mq_stop_hw_queues(ns->queue);
+		blk_mq_quiesce_queue(ns->queue);
 	}
 	mutex_unlock(&ctrl->namespaces_mutex);
 }