staging: comedi: addi-data: remove unused vars from private data

Due to the on-going cleanup of the addi-data drivers, the private
data used in the "common" code has a number of variables that
either are not used at all or or set but never used.

Remove all of them from the private data and the unnecessary use
in the 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>