cgroup: rstat: use same convention to assign cgroup_base_stat

In function cgroup_base_stat_flush(), we update cgroup_base_stat by
getting rstatc->bstat and adjust delta to related fields.

There are two convention to assign cgroup_base_stat in this function:

  * rstat2 = rstat1
  * rstat2.cputime = rstat1.cputime

The second convention may make audience think just field "cputime" is
updated, while cputime is the only field in cgroup_base_stat.

Let's use the same convention to eliminate this confusion.
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/cgroup/rstat.c

@@ -325,7 +325,7 @@ static void cgroup_base_stat_flush(struct cgroup *cgrp, int cpu)
 	/* fetch the current per-cpu values */
 	do {
 		seq = __u64_stats_fetch_begin(&rstatc->bsync);
-		cur.cputime = rstatc->bstat.cputime;
+		cur = rstatc->bstat;
 	} while (__u64_stats_fetch_retry(&rstatc->bsync, seq));
 
 	/* propagate percpu delta to global */