staging: comedi: cb_pcimdda: fix bug in call to subdev_8255_cleanup

The attach function only allocated 2 subdevices, an analog output
sundevice (index 0) and the 8255 dio subdevice (index 1). The
detach function is passing the wrong subdevice (index 2) to the
subdev_8255_cleanup function which will result in a bug when
it tries to do the kfree(s->private).

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>