cpumask: convert struct clock_event_device to cpumask pointers.

Impact: change calling convention of existing clock_event APIs

struct clock_event_timer's cpumask field gets changed to take pointer,
as does the ->broadcast function.

Another single-patch change.  For safety, we BUG_ON() in
clockevents_register_device() if it's not set.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Ingo Molnar <mingo@elte.hu>

arch/arm/mach-ixp4xx/common.c

@@ -487,7 +487,7 @@ static int __init ixp4xx_clockevent_init(void)
 		clockevent_delta2ns(0xfffffffe, &clockevent_ixp4xx);
 	clockevent_ixp4xx.min_delta_ns =
 		clockevent_delta2ns(0xf, &clockevent_ixp4xx);
-	clockevent_ixp4xx.cpumask = cpumask_of_cpu(0);
+	clockevent_ixp4xx.cpumask = cpumask_of(0);
 
 	clockevents_register_device(&clockevent_ixp4xx);
 	return 0;