staging: comedi: cb_pcimdda: minor cleanup of the private data

Remove the cut-and-paste comment from the skel driver and for
aesthetic reasons, move the #define out of the struct.

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>