staging: comedi: addi_apci_1516: remove use of struct addi_private

The only private data this driver has is the iobase address for the
watchdog. Create a local struct to hold this information in dev->private
and remove the need for struct addi_private from the "common" code.

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>