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>

kernel/sched_rt.c

@@ -225,7 +225,8 @@ static void set_curr_task_rt(struct rq *rq)
 	p->se.exec_start = rq->clock;
 }
 
-static struct sched_class rt_sched_class __read_mostly = {
+const struct sched_class rt_sched_class = {
+	.next			= &fair_sched_class,
 	.enqueue_task		= enqueue_task_rt,
 	.dequeue_task		= dequeue_task_rt,
 	.yield_task		= yield_task_rt,