staging: comedi: cb_pcidas: use dev->iobase for PCI bar 3

Currently the base address of the 8254 and 8255 devices, found in
PCI bar 3, is saved in the private data as 'pacer_counter_dio'.
The 'iobase' in the comedi_device is currently unused.

Save the address from PCI bar 3 in the comedi_device and remove
the unnecessary member from the private data.

This will help with some cleanup of the 8255 module.

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>