blk-sysfs: remove NULL pointer checking in queue_wb_lat_store

wbt_init doesn't set q->rq_wb to NULL, if wbt_init return 0,
so check return value is enough, remove NULL checking.
Signed-off-by: weiping zhang <zhangweiping@didichuxing.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-sysfs.c

@@ -450,12 +450,9 @@ static ssize_t queue_wb_lat_store(struct request_queue *q, const char *page,
 		ret = wbt_init(q);
 		if (ret)
 			return ret;
-
-		rwb = q->rq_wb;
-		if (!rwb)
-			return -EINVAL;
 	}
 
+	rwb = q->rq_wb;
 	if (val == -1)
 		rwb->min_lat_nsec = wbt_default_latency_nsec(q);
 	else if (val >= 0)