staging: comedi: icp_multi: tidy up the ADC command/status register bits

For aesthetics, rename these bit defines so they are associated with
the register and use the BIT macro to define them.

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>