staging: comedi: refactor dt282x driver to remove forward declarations

Move the struct comedi_driver and variables to the end of the
source. This is more typical of how other drivers are written and
removes the need for the forward declarations.

Convert the driver to use the module_comedi_driver() macro which
makes the code smaller and a bit simpler.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Mori Hess <fmhess@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>