staging: comedi: cb_pcimdda: use dev->iobase

Use dev->iobase for the pci i/o address instead of carrying it
in the private data.

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>