ide-disk: use ide_get_lba_addr()

* Export ide_get_lba_addr().

* Convert idedisk_{read_native,set}_max_address() to use ide_get_lba_addr().

* Remove incorrect comment from idedisk_read_native_max_address()
  (noticed by Sergei).

There should be no functionality changes caused by this patch.

Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>