staging: comedi: das800: move module_{init, exit} to end of file

The module_comedi_driver() macro provides the module_{init.exit}
code for this driver. Move the macro call and the comedi_driver
declaration to the end of the file. This also removes the need
for the das800_attach() forward declaration.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>