Block: blk-throttle: set low_valid immediately once one cgroup has io.low configured

Once one cgroup has io.low configured, @low_valid becomes true and other
cgroups won't switch it back whatsoever.
Signed-off-by: Liu Bo <bo.liu@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-throttle.c

@@ -579,8 +579,10 @@ static void blk_throtl_update_limit_valid(struct throtl_data *td)
 		struct throtl_grp *tg = blkg_to_tg(blkg);
 
 		if (tg->bps[READ][LIMIT_LOW] || tg->bps[WRITE][LIMIT_LOW] ||
-		    tg->iops[READ][LIMIT_LOW] || tg->iops[WRITE][LIMIT_LOW])
+		    tg->iops[READ][LIMIT_LOW] || tg->iops[WRITE][LIMIT_LOW]) {
 			low_valid = true;
+			break;
+		}
 	}
 	rcu_read_unlock();