ESP8266ComponentController: Add missing const in member functions

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

src/AutoPilotPlugins/Common/ESP8266ComponentController.h

@@ -63,7 +63,7 @@ public:
     QStringList     wifiChannels    () { return _channels; }
     QStringList     baudRates       () { return _baudRates; }
     int             baudIndex       ();
-    bool            busy            () { return _waitType != WAIT_FOR_NOTHING; }
+    bool            busy            () const{ return _waitType != WAIT_FOR_NOTHING; }
     Vehicle*        vehicle         () { return _vehicle; }
 
     void        setWifiSSID         (QString id);