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>
diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index 3566c00..dc81779 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -752,7 +752,7 @@
 	}
 	irq = -1;
 out:
-	spin_lock(&irq_mapping_update_lock);
+	spin_unlock(&irq_mapping_update_lock);
 
 	return irq;
 }