ide-cris: don't override ide_register_hw() result

* Don't override ide_register_hw() result and check if there is a hwif
  available to use.

* MAX_HWIFS is user configurable nowadays so replace it by hard-coded value.

* Remove the comment about ide_hwifs[].

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