AP_Terrain: correct compilation with rally disabled

libraries/AP_Terrain/AP_Terrain.cpp

@@ -345,8 +345,10 @@ void AP_Terrain::update(void)
     // check for pending mission data
     update_mission_data();
 
+#if HAL_RALLY_ENABLED
     // check for pending rally data
     update_rally_data();
+#endif
 
     // update tiles surrounding our current location:
     if (pos_valid) {

libraries/AP_Terrain/TerrainMission.cpp

@@ -115,6 +115,7 @@ void AP_Terrain::update_mission_data(void)
 #endif  // AP_MISSION_ENABLED
 }
 
+#if HAL_RALLY_ENABLED
 /*
   check that we have fetched all rally terrain data
  */
@@ -171,5 +172,6 @@ void AP_Terrain::update_rally_data(void)
         next_rally_index++;
     }
 }
+#endif
 
 #endif // AP_TERRAIN_AVAILABLE