[PATCH] hrtimer: call get_softirq_time() only when necessary in run_hrtimer_queue()

It seems that run_hrtimer_queue() is calling get_softirq_time() more
often than it needs to.

With this patch, it only calls get_softirq_time() if there's a
pending timer.

Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>