clockevents: Remove extra local_irq_save() in clockevents_exchange_device()

Called with 'clockevents_lock' held and interrupts disabled
already.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/51005827.yXt5tjZMBs@vostro.rjw.lan


Signed-off-by: Ingo Molnar <mingo@kernel.org>