[PATCH] ata_piix: ignore PCS on ICH5

There have been a number of reports regarding some ICH5s failing to
detect devices since the PCS handling update.  Analysis shows that
these problems are caused by bogus PCS values from those controllers.

Before the PCS update, the driver didn't honor PCS regs exactly and
probed them in many cases PCS reports no device.  Now that PCS is
honored exactly, these hardware problems are visible.

This patch makes ICH5 ignore PCS.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>