libata-link: linkify EH action helpers

Make ata_eh_about_to_do() and ata_eh_done() deal with ata_link instead
of ata_port.

This patch introduces no behavior change.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>