pata_sis: add missing UDMA5 timing value in sis_66_set_dmamode()

sis_66_set_dmamode() also handles early UDMA100 (SIS630 ET) but is
missing udma timing value for UDMA100.  According to sis5513, this
should be 0x8000.  This caused UDMA100 device to fail on pata_sis till
it downgrades to UDMA66 while it works fine on sis5513 at UDMA100.

Reported by Adam Blech.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Adam Blech <desaster.area@addcom.de>
Signed-off-by: Jeff Garzik <jeff@garzik.org>