pata_scc.c: Workaround for errata A308

Workaround for errata A308: turn down the UDMA mode and retry
the DMA command when the data lost condition is detected.

Signed-off-by: Kou Ishizaki <kou.ishizaki@toshiba.co.jp>
Signed-off-by: Akira Iguchi <akira2.iguchi@toshiba.co.jp>
Signed-off-by: Jeff Garzik <jeff@garzik.org>