cgroup: use tsk->in_iowait instead of delayacct_is_task_waiting_on_io()

If delayacct is disabled, then delayacct_is_task_waiting_on_io()
always returns false, which causes the statistical value to be
wrong. Perhaps tsk->in_iowait is better.
Signed-off-by: Chunguang Xu <brookxu@tencent.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/cgroup/cgroup-v1.c

@@ -727,7 +727,7 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
 			stats->nr_stopped++;
 			break;
 		default:
-			if (delayacct_is_task_waiting_on_io(tsk))
+			if (tsk->in_iowait)
 				stats->nr_io_wait++;
 			break;
 		}