cgroup: Avoid extra dereference in css_populate_dir()

Use css directly instead of dereferencing it from &cgroup->self, while
adding the cgroup v2 cft base and psi files in css_populate_dir(). Both
points to the same css, when css->ss is NULL, this avoids extra deferences
and makes code consistent in usage across the function.
Signed-off-by: Kamalesh Babulal <kamalesh.babulal@oracle.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/cgroup/cgroup.c

@@ -1719,13 +1719,13 @@ static int css_populate_dir(struct cgroup_subsys_state *css)
 
 	if (!css->ss) {
 		if (cgroup_on_dfl(cgrp)) {
-			ret = cgroup_addrm_files(&cgrp->self, cgrp,
+			ret = cgroup_addrm_files(css, cgrp,
 						 cgroup_base_files, true);
 			if (ret < 0)
 				return ret;
 
 			if (cgroup_psi_enabled()) {
-				ret = cgroup_addrm_files(&cgrp->self, cgrp,
+				ret = cgroup_addrm_files(css, cgrp,
 							 cgroup_psi_files, true);
 				if (ret < 0)
 					return ret;