cgroup: fix a typo in comment.

There is no function named cgroup_enable_task_cg_links().
Instead, the correct function name in this comment should
be cgroup_enabled_task_cg_lists().

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>