cgroup: s/cgroup_subsys_state/cgroup_css/ s/task_subsys_state/task_css/

The names of the two struct cgroup_subsys_state accessors -
cgroup_subsys_state() and task_subsys_state() - are somewhat awkward.
The former clashes with the type name and the latter doesn't even
indicate it's somehow related to cgroup.

We're about to revamp large portion of cgroup API, so, let's rename
them so that they're less awkward.  Most per-controller usages of the
accessors are localized in accessor wrappers and given the amount of
scheduled changes, this isn't gonna add any noticeable headache.

Rename cgroup_subsys_state() to cgroup_css() and task_subsys_state()
to task_css().  This patch is pure rename.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index e8aad69..87a0a03 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -58,12 +58,12 @@
 
 static inline struct dev_cgroup *cgroup_to_devcgroup(struct cgroup *cgroup)
 {
-	return css_to_devcgroup(cgroup_subsys_state(cgroup, devices_subsys_id));
+	return css_to_devcgroup(cgroup_css(cgroup, devices_subsys_id));
 }
 
 static inline struct dev_cgroup *task_devcgroup(struct task_struct *task)
 {
-	return css_to_devcgroup(task_subsys_state(task, devices_subsys_id));
+	return css_to_devcgroup(task_css(task, devices_subsys_id));
 }
 
 struct cgroup_subsys devices_subsys;