net: pcnet: Switch to PCI memory access

Replace the PCI IO access with PCI memory access, the card
supports both, but the former does not work with QEMU SH4.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Cc: Joe Hershberger <joe.hershberger@ni.com>