acpi: fix DMAR device scope for IOAPIC

We should not use cpu_to_le16() here, instead each of device/function
value is stored in a 8 byte field.

Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>