sched,irq: Convert to sched_set_fifo()

Because SCHED_FIFO is a broken scheduler model (see previous patches)
take away the priority field, the kernel can't possibly make an
informed decision.

Effectively no change.

Cc: tglx@linutronix.de
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>

kernel/irq/manage.c

@@ -1271,9 +1271,6 @@ static int
 setup_irq_thread(struct irqaction *new, unsigned int irq, bool secondary)
 {
 	struct task_struct *t;
-	struct sched_param param = {
-		.sched_priority = MAX_USER_RT_PRIO/2,
-	};
 
 	if (!secondary) {
 		t = kthread_create(irq_thread, new, "irq/%d-%s", irq,
@@ -1281,13 +1278,12 @@ setup_irq_thread(struct irqaction *new, unsigned int irq, bool secondary)
 	} else {
 		t = kthread_create(irq_thread, new, "irq/%d-s-%s", irq,
 				   new->name);
-		param.sched_priority -= 1;
 	}
 
 	if (IS_ERR(t))
 		return PTR_ERR(t);
 
-	sched_setscheduler_nocheck(t, SCHED_FIFO, &param);
+	sched_set_fifo(t);
 
 	/*
 	 * We keep the reference to the task struct even if