staging: comedi: refactor mpc624 driver and use module_comedi_driver

Move the struct comedi_driver and associated attach/detach
routines 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>