sched/core: Use list_is_singular() in sched_can_stop_tick()

Use list_is_singular() to check if run_list has only one entry.
Signed-off-by: NGeliang Tang <geliangtang@163.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/a5453fafd735affcf28e53a1d0a3d6965cb5dbb5.1447582547.git.geliangtang@163.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

kernel/sched/core.c

@@ -731,7 +731,7 @@ bool sched_can_stop_tick(void)
 	if (current->policy == SCHED_RR) {
 		struct sched_rt_entity *rt_se = &current->rt;
 
-		return rt_se->run_list.prev == rt_se->run_list.next;
+		return list_is_singular(&rt_se->run_list);
 	}
 
 	/*