staging: comedi: adl_pci9111: define a macro for the ai range bits

For aesthetics, define a macro to set the analog input range bits.

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>