xen: events: correct locking in xen_irq_from_pirq

One of those spin_lock() calls should be an unlock...
Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/xen/events.c

@@ -752,7 +752,7 @@ int xen_irq_from_pirq(unsigned pirq)
 	}
 	irq = -1;
 out:
-	spin_lock(&irq_mapping_update_lock);
+	spin_unlock(&irq_mapping_update_lock);
 
 	return irq;
 }