ahci: use ata_wait_after_reset() instead of ata_sff_wait_ready()

Implement ahci_check_ready() and replace ata_sff_wait_after_reset()
with ata_wait_after_reset().  As ahci was faking TF access, this
change doesn't result in any functional difference.

Signed-off-by: Tejun Heo <htejun@gmail.com>