staging: comedi: icp_multi: remove ao_maxdata from boardinfo

The analog outputs of this board always have 12-bit resolution.
Remove the boardinfo and just open-code the value.

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>