The only consumer uses it in a bogus manner, replace the use with an equivalent bogosity which does not require the field.
This also means getnewvnode takes the argument unnecessarily. I'll make a sweep to remove it later.
What you can do is (struct vnode *)(vp->v_object->handle) for object != NULL && object->type == OBJT_VNODE. The only case that would be not handled by this expression is nullfs mount over tmpfs.