pdc_adma: inherit ata_sff_port_ops

With the previous ops standardization, pdc_adma now can inherit
ata_sff_port_ops instead of ata_base_port_ops.  Make the change.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Mark Lord <liml@rtr.ca>
Signed-off-by: Jeff Garzik <jeff@garzik.org>