staging: comedi: adv_pci_dio: use the diosubd_data 'addr' for di/do s->private

Currently the di/do subdevices store a pointer to the diosubd_data in s->private.
The (*insn_bits) functions then use that to get to the 'addr' needed to access
the registers.

The only member of diosubd_data that is needed by the (*insn_bits) functions is
the 'addr'. For aesthetics, just store the 'addr' in s->private.

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>