staging: comedi: usbduxsigma: absorb usbduxsub_unlink_OutURBs() into caller

This function is only called by usbdux_ao_stop(). Absorb it.

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>