staging: comedi: refactor ssv_dnp driver and use module_comedi_driver

Move the module_init/module_exit routines and the associated
struct comedi_driver and other 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>