* Return 0 instead of dev->irq in ->init_chipset implementations.

* Fix ->init_chipset method to return 'int' value instead of
  'unsigned int' one.

This fixes ->init_chipset handling for host drivers (cs5530, hpt366
and pdc202xx_new) for which it is possible for this method to fail.
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>