staging: comedi: comedi_parport: remove 'a_data' from private data

Use the subdevice s->state to hold the current state of the data register
outputs instead of carrying it in the private data.

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>