Fixed warning

Fixes https://github.com/libsdl-org/SDL/issues/5842

src/video/winrt/SDL_winrtvideo.cpp

@@ -526,7 +526,7 @@ WINRT_DetectWindowFlags(SDL_Window * window)
 
 #if SDL_WINRT_USE_APPLICATIONVIEW
     if (data->appView) {
-        is_fullscreen = data->appView->IsFullScreen;
+        is_fullscreen = data->appView->IsFullScreenMode;
     }
 #elif (WINAPI_FAMILY == WINAPI_FAMILY_PHONE_APP) || (NTDDI_VERSION == NTDDI_WIN8)
     is_fullscreen = true;