cgroup: Fix kernel-doc

Fix function name in cgroup.c and rstat.c kernel-doc comment
to remove these warnings found by clang_w1.

kernel/cgroup/cgroup.c:2401: warning: expecting prototype for
cgroup_taskset_migrate(). Prototype was for cgroup_migrate_execute()
instead.
kernel/cgroup/rstat.c:233: warning: expecting prototype for
cgroup_rstat_flush_begin(). Prototype was for cgroup_rstat_flush_hold()
instead.
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Fixes: 'commit e595cd70 ("cgroup: track migration context in cgroup_mgctx")'
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/cgroup/cgroup.c

@@ -2389,7 +2389,7 @@ struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset,
 }
 
 /**
- * cgroup_taskset_migrate - migrate a taskset
+ * cgroup_migrate_execute - migrate a taskset
  * @mgctx: migration context
  *
  * Migrate tasks in @mgctx as setup by migration preparation functions.

kernel/cgroup/rstat.c

@@ -220,7 +220,7 @@ void cgroup_rstat_flush_irqsafe(struct cgroup *cgrp)
 }
 
 /**
- * cgroup_rstat_flush_begin - flush stats in @cgrp's subtree and hold
+ * cgroup_rstat_flush_hold - flush stats in @cgrp's subtree and hold
  * @cgrp: target cgroup
  *
  * Flush stats in @cgrp's subtree and prevent further flushes.  Must be