staging: comedi: addi_apci_3120: remove boardinfo 'i_DoMaxdata'

The maxdata for a Digital Output subdevice is always '1'. Remove this
incorrect boardinfo.

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>