staging: comedi: refactor adq12b driver to remove forward declarations

Move the module_init/module_exit routines and the associated
struct comedi_driver and struct boardtype variables to the end
of the source as is more typically done with other drivers. Then
rearrange the attach/detach functions, this removes the need
for all the forward declarations.

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>