sata_via: Correctly setup PIO/DMA for pata slave on vt6421.

Before only the timings for master were set. Datasheet can be found
here: ftp://ftp.vtbridge.org/Docs/Storage/DS_VT6421A_100_CCPL.PDF
Surprisingly, a slave drive works without this patch. According to the
datasheet, the controller by default derives the DMA mode from the
Set Features command issued to a drive. Not sure about the PIO
timings, though. The real problem is that the timings for the master
effectively are the ones tuned for the slave. If these support
different UDMA-settings, there is trouble, especially when the slave
supports a higher UDMA than the master.

Anyhow, using the same mechanism for both master and slave seems like
a good idea.

Signed-off-by: Bart Hartgers <bart.hartgers@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>