sata_via: kill SATA_PATA_SHARING register handling

The SATA_PATA_SHARING register doesn't have anything to do with the
SATA part of the controller.  It indicates whether an extern SATA PHY
is attached to the PATA part of the controller and if so how it is
wired.  As the PATA part is driven by pata_via, sata_via has no reason
to care about that.  Also, pata_via should work fine under all
configurations.

This patch removes unnecessary attach failures.  It seems recent via
chipsets are defaulting to different values or are actually connected
to SATA PHY triggering this more often.

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