Rover: frsky telem init to utilize default arguments

APMrover2/system.cpp

@@ -129,7 +129,7 @@ void Rover::init_ardupilot()
 
     // setup frsky telemetry
 #if FRSKY_TELEM_ENABLED == ENABLED
-    frsky_telemetry.init(serial_manager, FIRMWARE_STRING, MAV_TYPE_GROUND_ROVER, nullptr, nullptr, nullptr);
+    frsky_telemetry.init(serial_manager, FIRMWARE_STRING, MAV_TYPE_GROUND_ROVER);
 #endif
 
     mavlink_system.sysid = g.sysid_this_mav;