sched,acpi_pad: 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.

In this case, use fifo_low, because it only cares about being above
SCHED_NORMAL. Effectively no change in behaviour.

XXX: this driver is still complete crap; why isn't it using proper
idle injection or at the very least play_idle() ?

Cc: rafael.j.wysocki@intel.com
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>

drivers/acpi/acpi_pad.c

@@ -136,12 +136,11 @@ static unsigned int idle_pct = 5; /* percentage */
 static unsigned int round_robin_time = 1; /* second */
 static int power_saving_thread(void *data)
 {
-	struct sched_param param = {.sched_priority = 1};
 	int do_sleep;
 	unsigned int tsk_index = (unsigned long)data;
 	u64 last_jiffies = 0;
 
-	sched_setscheduler(current, SCHED_RR, &param);
+	sched_set_fifo_low(current);
 
 	while (!kthread_should_stop()) {
 		unsigned long expire_time;