xen/irq: Cleanup up the pirq_to_irq for DomU PV PCI passthrough guests as well.

We only did this for PV guests that are xen_initial_domain() but
there is not reason not to do this for other cases. The other
case is only exercised when you pass in a PCI device to a PV guest
_and_ the device in question.
Reviewed-by: NIan Campbell <ian.campbell@citrix.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/xen/events.c

@@ -766,8 +766,9 @@ int xen_destroy_irq(int irq)
 			printk(KERN_WARNING "unmap irq failed %d\n", rc);
 			goto out;
 		}
-		pirq_to_irq[info->u.pirq.pirq] = -1;
 	}
+	pirq_to_irq[info->u.pirq.pirq] = -1;
+
 	irq_info[irq] = mk_unbound_info();
 
 	xen_free_irq(irq);