staging: comedi: cb_pcidda: cleanup the dio register defines

Remove the unused defines for the dio registers. Add two new
defines to document the iobase registers for the two 8255 devices.

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