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>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 548d8d4..bab5c17 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2175,9 +2175,12 @@
 		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;
+		}
 	}
 
 	/*