Incorrect LSB for __Memoize on static functions

``` Hack
>
protected static function doStuff() {
var_dump(static::class);
}
}

class B extends A {
public static function doOtherStuff() {
self::doStuff();
}
}

B::doOtherStuff();
```

Actual output: A
Expected output: B

From bytecode:

```
55: FPushClsMethodD 0 "doStuff$memoize_impl" "A"
```

This should be FPushClsMethodF.

The user still needs to be careful about the shared cache between the superclass and child class