Convert ata_pio_task() to use the new ata_hsm_move().

Changes:
- refactor ata_pio_task() to poll device status register and
- call the new ata_hsm_move() when device indicates it is not BSY.
Signed-off-by: NAlbert Lee <albertcc@tw.ibm.com>
Signed-off-by: NJeff Garzik <jeff@garzik.org>