Copter: init_compass get g.compass_enabled check

No functional change

ArduCopter/sensors.cpp

@@ -100,6 +100,10 @@ void Copter::rpm_update(void)
 // initialise compass
 void Copter::init_compass()
 {
+    if (!g.compass_enabled) {
+        return;
+    }
+
     if (!compass.init() || !compass.read()) {
         // make sure we don't pass a broken compass to DCM
         cliSerial->printf("COMPASS INIT ERROR\n");

ArduCopter/system.cpp

@@ -207,8 +207,7 @@ void Copter::init_ardupilot()
     // Do GPS init
     gps.init(&DataFlash, serial_manager);
 
-    if(g.compass_enabled)
-        init_compass();
+    init_compass();
 
 #if OPTFLOW == ENABLED
     // make optflow available to AHRS