rename CreateAudioDevice to GetAudioDevice

main/boards/kevin-box-0/kevin_box_board.cc

@@ -68,8 +68,9 @@ public:
         Ml307Board::Initialize();
     }
 
-    virtual AudioDevice* CreateAudioDevice() override {
-        return new BoxAudioDevice();
+    virtual AudioDevice* GetAudioDevice() override {
+        static BoxAudioDevice audio_device;
+        return &audio_device;
     }
 
     virtual bool GetBatteryVoltage(int &voltage, bool& charging) override {