staging: comedi: usbdux: use attach_usb() hook

Change the usbdux driver to use the new attach_usb() hook in struct
comedi_driver to auto-configure probed USB devices after the firmware is
loaded.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>