staging: comedi: ni_mio_common: remove forward declaration 6

Move the ni_gpct_cmd() and ni_gpct_cancel() functions to remove the
need for the forward declarations.

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>