staging: comedi: cb_pcidas: convert inline DAC bit helpers to macros

For aesthetics, convert the inline functions that return the bits
used to set the DAC range and enable bits to macros.

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>