sched,serial: 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.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>

drivers/tty/serial/sc16is7xx.c

@@ -1179,7 +1179,6 @@ static int sc16is7xx_probe(struct device *dev,
 			   const struct sc16is7xx_devtype *devtype,
 			   struct regmap *regmap, int irq)
 {
-	struct sched_param sched_param = { .sched_priority = MAX_RT_PRIO / 2 };
 	unsigned long freq = 0, *pfreq = dev_get_platdata(dev);
 	unsigned int val;
 	u32 uartclk = 0;
@@ -1239,7 +1238,7 @@ static int sc16is7xx_probe(struct device *dev,
 		ret = PTR_ERR(s->kworker_task);
 		goto out_clk;
 	}
-	sched_setscheduler(s->kworker_task, SCHED_FIFO, &sched_param);
+	sched_set_fifo(s->kworker_task);
 
 #ifdef CONFIG_GPIOLIB
 	if (devtype->nr_gpio) {