cgroup: move assignement out of condition in cgroup_attach_proc()

Gcc complains about this: "kernel/cgroup.c:2179:4: warning: suggest
parentheses around assignment used as truth value [-Wparentheses]"
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/cgroup.c

@@ -2175,10 +2175,13 @@ static int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
 		oldcg = tc->task->cgroups;
 
 		/* if we don't already have it in the list get a new one */
-		if (!css_set_check_fetched(cgrp, tc->task, oldcg, &newcg_list))
-			if (retval = css_set_prefetch(cgrp, oldcg, &newcg_list))
+		if (!css_set_check_fetched(cgrp, tc->task, oldcg,
+					   &newcg_list)) {
+			retval = css_set_prefetch(cgrp, oldcg, &newcg_list);
+			if (retval)
 				goto out_list_teardown;
 		}
+	}
 
 	/*
 	 * step 3: now that we're guaranteed success wrt the css_sets,