APMSubFrameComponent.qml: update to use versionCompare()

src/AutoPilotPlugins/APM/APMSubFrameComponent.qml

@@ -25,7 +25,7 @@ SetupPage {
     pageComponent:      subFramePageComponent
 
     property var  _activeVehicle:       QGroundControl.multiVehicleManager.activeVehicle
-    property bool _oldFW:   !(_activeVehicle.firmwareMajorVersion > 3 || _activeVehicle.firmwareMinorVersion > 5 || _activeVehicle.firmwarePatchVersion >= 2)
+    property bool _oldFW:   _activeVehicle.versionCompare(3 ,5 ,2) < 0
 
     APMAirframeComponentController { id: controller; factPanel: subFramePage.viewPanel }