staging: comedi: dt282x: convert private data flags to bit-fields

Convert the '2scomp' flags in the private data into bit-fields to save
a bit of space.

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>