xen: fix trivial PCI passthrough MSI-X bug

We are currently passing entry->data as address parameter. Pass
entry->addr instead.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Tested-by: Sander Eikelenboom <linux@eikelenboom.it>
Xen-devel: http://marc.info/?l=xen-devel&m=135515462613715