clockevents: optimise tick_nohz_stop_sched_tick() a bit

Call
	ts = &per_cpu(tick_cpu_sched, cpu);
and
	cpu = smp_processor_id();
once instead of twice.

No functional change done, as changed code runs with local irq off.
Reduces source lines and text size (20bytes on x86_64).

[ akpm@linux-foundation.org: Build fix ]
Signed-off-by: Karsten Wiese <fzu@wemgehoertderstaat.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/time/tick-sched.c

@@ -158,9 +158,8 @@ void tick_nohz_stop_idle(int cpu)
 	}
 }
 
-static ktime_t tick_nohz_start_idle(int cpu)
+static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
 {
-	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
 	ktime_t now, delta;
 
 	now = ktime_get();
@@ -201,8 +200,8 @@ void tick_nohz_stop_sched_tick(void)
 	local_irq_save(flags);
 
 	cpu = smp_processor_id();
-	now = tick_nohz_start_idle(cpu);
 	ts = &per_cpu(tick_cpu_sched, cpu);
+	now = tick_nohz_start_idle(ts);
 
 	/*
 	 * If this cpu is offline and it is the one which updates
@@ -222,7 +221,6 @@ void tick_nohz_stop_sched_tick(void)
 	if (need_resched())
 		goto end;
 
-	cpu = smp_processor_id();
 	if (unlikely(local_softirq_pending())) {
 		static int ratelimit;