staging: comedi: ii_pci20kc: use the comedi_device 'mmio' member

Use the new 'mmio' member in the comedi_device for the __iomem * base
address.

Since this was the only member in the private data, remove the struct
and its allocation.

This legacy driver is a bit strange. The base address of the board is
passed to the (*attach) using by the user using the comedi_config
utiltiy. This base address is currently not ioremap'ed and is simply
cast to a void __iomem *. I'm not sure if this is correct. Add a
comment so it will be addressed later.

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>