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>
diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
index eccefbb..f5bd141 100644
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -154,7 +154,7 @@
 	cd->min_delta_ns	= 1;
 	cd->max_delta_ns	= LONG_MAX;
 	cd->rating		= 400;
-	cd->cpumask		= cpumask_of_cpu(cpu);
+	cd->cpumask		= cpumask_of(cpu);
 	cd->set_next_event	= s390_next_event;
 	cd->set_mode		= s390_set_mode;