sched: mark scheduling classes as const

mark scheduling classes as const. The speeds up the code
a bit and shrinks it:

   text    data     bss     dec     hex filename
  40027    4018     292   44337    ad31 sched.o.before
  40190    3842     292   44324    ad24 sched.o.after

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 97f736b..47e3717 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -863,7 +863,7 @@
 struct sched_domain;
 
 struct sched_class {
-	struct sched_class *next;
+	const struct sched_class *next;
 
 	void (*enqueue_task) (struct rq *rq, struct task_struct *p, int wakeup);
 	void (*dequeue_task) (struct rq *rq, struct task_struct *p, int sleep);
@@ -949,7 +949,7 @@
 
 	int prio, static_prio, normal_prio;
 	struct list_head run_list;
-	struct sched_class *sched_class;
+	const struct sched_class *sched_class;
 	struct sched_entity se;
 
 #ifdef CONFIG_PREEMPT_NOTIFIERS