xen: Remove unnecessary BUG_ON from __unbind_from_irq()

Commit 910f8bef ("xen/pirq: fix error path cleanup when binding
MSIs") fixed a couple of errors in error cleanup path of
xen_bind_pirq_msi_to_irq(). This cleanup allowed a call to
__unbind_from_irq() with an unbound irq, which would result in
triggering the BUG_ON there.

Since there is really no reason for the BUG_ON (xen_free_irq() can
operate on unbound irqs) we can remove it.
Reported-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: stable@vger.kernel.org
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>

drivers/xen/events/events_base.c

@@ -628,8 +628,6 @@ static void __unbind_from_irq(unsigned int irq)
 		xen_irq_info_cleanup(info);
 	}
 
-	BUG_ON(info_for_irq(irq)->type == IRQT_UNBOUND);
-
 	xen_free_irq(irq);
 }