ide: add hwif_register_devices() helper

Add hwif_register_devices() helper to fix code duplication between
probe_hwif_init_with_fixup() and ideprobe_init().  Also remove stale
comment while at it.

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