* always call __ide_do_rw_disk() in ide_do_rw_disk()
* modify ide_hwif_t->rw_disk hook accordingly
* update and cleanup hpt372n_rw_disk()
  (the only user of ide_hwif_t->rw_disk hook)
* make __ide_do_rw_disk() static + fix comment
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>