8139too: Force usage of PIO on OQO2

The OQO model 2 has an RTL8139 from Atheros that doesn't like MMIO.
It fails on modprobe, with a 'PCI Bus error' message.

Force it to always use polled IO.

Signed-off-by: Dave Jones <davej@redhat.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>