Rover: pre_arm_gps_check flag always true

APMrover2/APMrover2.pde

@@ -548,6 +548,7 @@ void setup() {
     // rover does not use arming nor pre-arm checks
     AP_Notify::flags.armed = true;
     AP_Notify::flags.pre_arm_check = true;
+    AP_Notify::flags.pre_arm_gps_check = true;
     AP_Notify::flags.failsafe_battery = false;
 
     notify.init(false);