sis5513: backport short cables support from pata_sis.c

Backport short cables support from pata_sis.c.

This patch allows UDMA > 2 modes on ASUS A6K.

Thanks to testing this patch goes out to Jiri Stavinoha.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>