ide: remove chipset type fixup from ide_host_register()

* Set chipset type explicitly in tx4938ide and tx4939ide host drivers
  (all other host drivers were updated already).

* Remove no longer used chipset type fixup from ide_host_register().

Acked-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Cc: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>