hrtimer: optimize the softirq time optimization

The previous optimization did not take the case into account where a
clock provides its own softirq_get_time() function.

Check for the availablitiy of the clock get time function first and
then check if we need to retrieve the time for both clocks via
hrtimer_softirq_gettime() to avoid a double evaluation of time in that
case as well.
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

kernel/hrtimer.c

@@ -1254,14 +1254,13 @@ void hrtimer_run_queues(void)
 		if (!base->first)
 			continue;
 
-		if (gettime) {
+		if (base->get_softirq_time)
+			base->softirq_time = base->get_softirq_time();
+		else if (gettime) {
 			hrtimer_get_softirq_time(cpu_base);
 			gettime = 0;
 		}
 
-		if (base->get_softirq_time)
-			base->softirq_time = base->get_softirq_time();
-
 		spin_lock(&cpu_base->lock);
 
 		while ((node = base->first)) {