staging: comedi: ni_tio: convert global static const variables to defines

For aesthetics, convert the global static const varaibles into defines.

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>