sched: fix the wrong time slice value for SCHED_FIFO tasks

Function sys_sched_rr_get_interval returns wrong time slice value for
SCHED_FIFO tasks. The time slice for SCHED_FIFO tasks should be 0.
Signed-off-by: NMiao Xie <miaox@cn.fujitsu.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

kernel/sched.c

@@ -5100,7 +5100,7 @@ long sys_sched_rr_get_interval(pid_t pid, struct timespec __user *interval)
 	time_slice = 0;
 	if (p->policy == SCHED_RR) {
 		time_slice = DEF_TIMESLICE;
-	} else {
+	} else if (p->policy != SCHED_FIFO) {
 		struct sched_entity *se = &p->se;
 		unsigned long flags;
 		struct rq *rq;