AP_Tuning: compile warning: float to double on print

libraries/AP_Tuning/AP_Tuning.cpp

@@ -333,7 +333,7 @@ void AP_Tuning::check_controller_error(void)
         uint32_t now = AP_HAL::millis();
         if (now - last_controller_error_ms > 2000) {
             AP_Notify::events.tune_error = 1;
-            GCS_MAVLINK::send_statustext_all(MAV_SEVERITY_INFO, "Tuning: error %.2f", err);
+            GCS_MAVLINK::send_statustext_all(MAV_SEVERITY_INFO, "Tuning: error %.2f", (double)err);
             last_controller_error_ms = now;
         }
     }