Restored the previously suppressed __attribute__ unused in a portable way

plugins/samplesource/limesdrinput/limesdrinputplugin.cpp

@@ -116,6 +116,9 @@ PluginInstanceGUI* LimeSDRInputPlugin::createSampleSourcePluginInstanceGUI(
         QWidget **widget,
         DeviceUISet *deviceUISet)
 {
+    (void) sourceId;
+    (void) widget;
+    (void) deviceUISet;
     return 0;
 }
 #else