gdk: wayland: always set buffer scale on size update

We're only updating this when we have an EGL window. This means we
have the wrong scaling factor when using Vulkan.

https://bugzilla.gnome.org/show_bug.cgi?id=786492

gdk/wayland/gdkwindow-wayland.c

@@ -336,8 +336,8 @@ gdk_wayland_window_update_size (GdkWindow *window,
                             width * scale,
                             height * scale,
                             0, 0);
-      wl_surface_set_buffer_scale (impl->display_server.wl_surface, scale);
     }
+  wl_surface_set_buffer_scale (impl->display_server.wl_surface, scale);
 
   area.x = 0;
   area.y = 0;