Fix Python3 binding's submodules
Fix Python3 binding's submodules

Previously the Python3 cv2 package ends up with no submodules (bgsegm, face,
etc) in it, which makes a lot of functionality unusable. By not writing over
our root reference we ensure the new submodules are added to the correct cv2
module.

opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv