staging: comedi: amplc_dio200: use the comedi_device 'mmio' member

The amplc_dio200_common module currently uses a union in the private
data to determine if the hardware uses port or memory mapped I/O.

Use the new 'mmio' member in the comedi_device for the ioremap'ed
base address and remove all the union 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>