ide: remove ->data_phase field from ide_hwif_t

* Always use hwif->task->data_phase and remove ->data_phase
  field from ide_hwif_t.

* Remove superfluous REQ_TYPE_ATA_TASKFILE check from
  ide_pio_datablock() while at it.

There should be no functional changes caused by this patch.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>