staging: comedi: usbdux: consolidate usbduxsub_unlink_{in, out}urbs()

These functions are identical other than the which and how many urbs
are unlinked.

Consolidate the functions into one usbdux_unlink_urbs() function.

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>