Fix double-buffering for spi display (it's actually using double-buffering, now)

src/DisplayApp/DisplayApp.cpp

@@ -45,6 +45,9 @@ void DisplayApp::Process(void *instance) {
   NRF_LOG_INFO("DisplayApp task started!");
   app->InitHw();
 
+  // Send a dummy notification to unlock the lvgl display driver for the first iteration
+  xTaskNotifyGive(xTaskGetCurrentTaskHandle());
+
   while (1) {
 
     app->Refresh();