staging: comedi: hwdrv_apci2200: remove forward declarations

None of the functions in this file are exported. Make all of them
static and remove the unnecessary forward declarations.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>