(2.6.20) pata_oldpiix: fix PIO2 underclocking

Fix the PIO mode 2 using mode 0 timings -- this driver should enable the
fast timing bank starting with PIO2, just like the ata_piix driver does.
Also, fix/rephrase some comments while at it.

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>