nvme: update comment to make the code easier to read

After commit a686ed75 ("nvme: introduce a helper function for
controller deletion), nvme_delete_ctrl_sync no longer use flush_work.
Update comment, accordingly.
Signed-off-by: Yufen Yu <yuyufen@huawei.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/nvme/host/core.c

@@ -179,8 +179,8 @@ static int nvme_delete_ctrl_sync(struct nvme_ctrl *ctrl)
 	int ret = 0;
 
 	/*
-	 * Keep a reference until the work is flushed since ->delete_ctrl
-	 * can free the controller.
+	 * Keep a reference until nvme_do_delete_ctrl() complete,
+	 * since ->delete_ctrl can free the controller.
 	 */
 	nvme_get_ctrl(ctrl);
 	if (!nvme_change_ctrl_state(ctrl, NVME_CTRL_DELETING))