pata_hpt3x3: Workarounds for chipset

Correct the DMA bit flags (UDMA and MWDMA were swapped)
Add workarounds so that we clear ERR and INTR bits before issuing a DMA
Add workarounds so that we stop a live DMA before touching the CTL register

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>