staging: comedi: refactor the adl_pci6208 driver to remove the forward declarations

Move the module_init/module_exit routines and variables to the
end of the source as is more typically done with other drivers.
Then rearrange the attach/detach and probe/remove 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>