joint: Unify return type documentation
joint: Unify return type documentation

Make sure all return type fields link to the object correctly.

GNOME/clutter-box2d,GNOME/clutter-box2d,GNOME/clutter-box2d,clutter-project/clutter-box2d,GNOME/clutter-box2d,clutter-project/clutter-box2d,clutter-project/clutter-box2d,clutter-project/clutter-box2d