xen: compilation fix of drivers/xen/events.c on IA64

use set_xen_guest_handle() instead of direct assigning.

> linux-2.6/drivers/xen/events.c: In function 'xen_poll_irq':
> linux-2.6/drivers/xen/events.c:757: error: incompatible types in assignment
> make[4]: *** [drivers/xen/events.o] Error 1

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

drivers/xen/events.c

@@ -774,7 +774,7 @@ void xen_poll_irq(int irq)
 
 		poll.nr_ports = 1;
 		poll.timeout = 0;
-		poll.ports = &evtchn;
+		set_xen_guest_handle(poll.ports, &evtchn);
 
 		if (HYPERVISOR_sched_op(SCHEDOP_poll, &poll) != 0)
 			BUG();