staging: comedi: addi_apci_3xxx: analog output 'maxdata' is always 12-bit

The boards that have analog outputs always have 12-bit resolution.

Remove the 'i_AoMaxdata' data from the boardinfo and open code the
s->maxdata. Use the hex value for the resolution since that is more
common in comedi drivers.

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>