staging: comedi: usbdux: remove the SUBDEV_* defines

These defines are only used to index the dev->subdevices array
during the attach. It's cleaner to just open-code the values.

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>