pata_scc.c: small fixes (Workaround for errata A308)

This patch fixes some issues of the previous patch:
- Use mode_filter() hook to limit ATAPI UDMA mode
- "data loss" warning message
- handling of udma_mask

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>