staging: comedi: partial refactor of the rtd520 driver to remove forward declarations

Move the struct comedi_driver MODULE_DEVICE_TABLE to the end
of the source. The attach and detach functions are not moved yet
because patch is pretty messy and not reviewable. This is more
typical of how other drivers are written and removes the need for
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>