message: telemetry: fix accidental change
  In the previous commit, we accidentally changed the init value of this
  variable, therefore we change it back.
diff: @@ -197,7 +197,7 @@ private:
  // The ground speed and position are coupled to the same message, therefore, we just use
  // the faster between the two.
  - double _ground_speed_ned_rate_hz{1.0};
  + double _ground_speed_ned_rate_hz{0.0};
  double _position_rate_hz{-1.0};
  void *_timeout_cookie{nullptr};
  