staging: comedi: cb_das16_cs: add module_{init, exit} declarations

The init and exit functions for this module were being declared
as global symbols. Add the module_{init,exit} declarations and
make the functions static. Also, rename the functions so they
have namespace associated with the module.

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