Sub: use compass singleton for logging

ArduSub/ArduSub.cpp

@@ -175,7 +175,7 @@ void Sub::update_batt_compass()
         compass.read();
         // log compass information
         if (should_log(MASK_LOG_COMPASS) && !ahrs.have_ekf_logging()) {
-            DataFlash.Log_Write_Compass(compass);
+            DataFlash.Log_Write_Compass();
         }
     }
 }