pata_efar: fix wrong PIO timings being programmed

* do not clear PIO timings for master when programming slave
* do not clear PIO timings for device on the other port when
  programming slave device

Both changes should be safe as this is how we have been doing
things in IDE slc90e66 host driver for years.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>