staging: comedi: cb_pcidas64: fix forward declarations 1

Move `setup_subdevices()` and remove a load of forward declarations.
Added a forward declaration of `setup_subdevices()` temporarily.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>