cgroup: remove sparse tags from offline_css()

This should have been removed in commit d7eeac1913ff
("cgroup: hold cgroup_mutex before calling css_offline").

While at it, update the comments.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
1 file changed