Copter: correct definition of unused variable when precision landing disabled

ArduCopter/mode_land.cpp

@@ -158,9 +158,8 @@ int32_t Copter::ModeLand::get_alt_above_ground(void)
 
 void Copter::land_run_vertical_control(bool pause_descent)
 {
-    bool navigating = pos_control->is_active_xy();
-
 #if PRECISION_LANDING == ENABLED
+    const bool navigating = pos_control->is_active_xy();
     bool doing_precision_landing = !ap.land_repo_active && precland.target_acquired() && navigating;
 #else
     bool doing_precision_landing = false;