xen/events: use locked set|clear_bit() for cpu_evtchn_mask

The per-cpu event channel masks can be updated unlocked from multiple
CPUs, so use the locked variant.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index d770b8c..d6d4f76 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -278,8 +278,8 @@
 	cpumask_copy(irq_to_desc(irq)->affinity, cpumask_of(cpu));
 #endif
 
-	__clear_bit(chn, cpu_evtchn_mask(cpu_from_irq(irq)));
-	__set_bit(chn, cpu_evtchn_mask(cpu));
+	clear_bit(chn, cpu_evtchn_mask(cpu_from_irq(irq)));
+	set_bit(chn, cpu_evtchn_mask(cpu));
 
 	irq_info[irq].cpu = cpu;
 }