xen: events: Fix compile error if CONFIG_SMP is not defined.

drivers/xen/events.c:396: error: 'struct irq_data' has no member named 'affinity'
Reported-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/xen/events.c

@@ -392,8 +392,10 @@ static void xen_irq_init(unsigned irq)
 	struct irq_info *info;
 	struct irq_desc *desc = irq_to_desc(irq);
 
+#ifdef CONFIG_SMP
 	/* By default all event channels notify CPU#0. */
 	cpumask_copy(desc->irq_data.affinity, cpumask_of(0));
+#endif
 
 	info = kzalloc(sizeof(*info), GFP_KERNEL);
 	if (info == NULL)