pata_sis: Fix and clean up some timing setups

- Rename sis_port_base to sis_old_port_base() so nobody uses it for new
generation controllers in error.
- Use byte size operations where it is cleaner for mode setup
- Fix a couple of masking errors on certai chip revs when setting speeds

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>