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 <[email protected]>
Acked-by: Paul Menage <[email protected]>
Acked-by: Paul Turner <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

Author: Glauber Costa

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 */