staging: comedi: pcmuio: remove 'iobases' from subdevice private data

The 'asic' and 'port' associated with a given subdevice can easily be
found based on the subdevice 'index'. With that information we can
then calculate the correct iobase and register offset needed to read/
write the 8-bit ports.

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>