staging: comedi: dt9812: move shadow values to private data

The analog and digital out shadow values are only used by the
comedi_device. Move the variables from the usb private data to
the comedi private data. Also, rename them to something a bit
shorter.

Move the initialization of the shadow values from the usb probe
to the comedi attach. Also rename the flag used to determine the
initial value from 'range_2_5' to 'is_unipolar'.

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>