sched, trivial: Initialize root cgroup's sibling list

Even though there are no siblings, the list should be
initialized to not contain bogus values.

Signed-off-by: Glauber Costa <glommer@parallels.com>
Acked-by: Paul Menage <paul@paulmenage.org>
Acked-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1320182360-20043-2-git-send-email-glommer@parallels.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched.c

@@ -8275,6 +8275,7 @@ void __init sched_init(void)
 #ifdef CONFIG_CGROUP_SCHED
 	list_add(&root_task_group.list, &task_groups);
 	INIT_LIST_HEAD(&root_task_group.children);
+	INIT_LIST_HEAD(&root_task_group.siblings);
 	autogroup_init(&init_task);
 #endif /* CONFIG_CGROUP_SCHED */