clockevents: Set noop handler in clockevents_exchange_device()

If a device is shutdown, then there might be a pending interrupt,
which will be processed after we reenable interrupts, which causes the
original handler to be run. If the old handler is the (broadcast)
periodic handler the shutdown state might hang the kernel completely.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org

kernel/time/clockevents.c

@@ -387,6 +387,7 @@ void clockevents_exchange_device(struct clock_event_device *old,
 	 * released list and do a notify add later.
 	 */
 	if (old) {
+		old->event_handler = clockevents_handle_noop;
 		clockevents_set_mode(old, CLOCK_EVT_MODE_UNUSED);
 		list_del(&old->list);
 		list_add(&old->list, &clockevents_released);