framework: fix rvalue reference warnings

[PragmaTwice]

To fix this error reported by Clang:

home/twice/project/oneflow/oneflow/core/framework/tensor_consistent_id.h:43:12: error: local variable 'ret' will be copied despite being returned by name [-Werror,-Wreturn-std-move]
    return ret;
           ^~~

In this case, create an rvalue reference and return it (as lvalue) can cause a copy initialization.
I made an example to illuminate this behavior:

struct X {
    X() { std::cout << "X\n"; }
    X(const X&) { std::cout << "const X&\n"; }
    X(X&&) { std::cout << "X&&\n"; } 
};

X g() {
    return X();
}

X f() {
    X x = g();      // case 1
    // X&& x = g(); // case 2
    return x;
}

int main() {
    X a = f();
}

In case 2, we will find an unnecessary X(const X&) will be called.
You can open https://godbolt.org/z/a91c1snza to debug this example online.