staging: comedi: use module_comedi_driver

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

In the process, rename the driver variables from driver_* to *_driver,
as is more typical with other subsystems, and make sure they are all
static.

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