md/raid10: don't modify 'nr_waitng' in wait_barrier() for the case nowait

For the case nowait in wait_barrier(), there is no point to increase
nr_waiting and then decrease it.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Acked-by: Guoqing Jiang <guoqing.jiang@linux.dev>
Signed-off-by: Song Liu <song@kernel.org>

drivers/md/raid10.c

@@ -990,17 +990,17 @@ static bool wait_barrier(struct r10conf *conf, bool nowait)
 
 	spin_lock_irq(&conf->resync_lock);
 	if (conf->barrier) {
-		conf->nr_waiting++;
 		/* Return false when nowait flag is set */
 		if (nowait) {
 			ret = false;
 		} else {
+			conf->nr_waiting++;
 			raid10_log(conf->mddev, "wait barrier");
 			wait_event_lock_irq(conf->wait_barrier,
 					    stop_waiting_barrier(conf),
 					    conf->resync_lock);
-		}
 			conf->nr_waiting--;
+		}
 		if (!conf->nr_waiting)
 			wake_up(&conf->wait_barrier);
 	}