ide: sanitize ide_unregister() usage

* Remove ide_unregister() call from ide_exit()
  (host drivers take care of unregistering hwif-s themselves).

* Remove ide_unregister() call from probe methods of
  bast-ide, palm_bk3710, ide-cs and delkin_cb host drivers
  (ide_find_port() returns only free ide_hwifs[] entries).

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