staging: comedi: adv_pci_dio: cleanup PCI-175[46] interrupt registers

For aesthetics, replace these defines with a macro.

Refactor the switch in pci_dio_reset() to use common code.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>