ide-pmac: fix pmac_ide_init_hwif_ports()

* pmac_ide_init_hwif_ports() can be called by ide_init_hwif_ports()
  (through ppc_ide_md.ide_init_hwif hook) for non IDE PMAC interfaces.
  If this is the case the hw->io_ports[] should be already setup by
  ide_init_hwif_ports()->ide_std_init_ports() so remove redundant code
  from pmac_ide_init_hwif_ports().

  As side-effect this change fixes ctl_addr == 0 special handling in
  ide_init_hwif_ports().

* Fix misleading comment while at it.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>