(2.6.20) pata_mpiix: fix PIO setup issues

Fix clearing/setting the wrong TIME/IE/PPE bits for a slave drive caused by a
wrong shift count.
Fix the PIO mode 1 being overclocked by wrongly selecting the fast timing bank.
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>