simple-egl: Set the right size for the opaque region when fullscreen

window.window_size holds the size of the window in windowed mode. Use
window.geometry for setting the opaque region since that holds the
current size.

clients/simple-egl.c

@@ -409,8 +409,8 @@ redraw(void *data, struct wl_callback *callback, uint32_t time)
 	if (window->opaque || window->fullscreen) {
 		region = wl_compositor_create_region(window->display->compositor);
 		wl_region_add(region, 0, 0,
-			      window->window_size.width,
-			      window->window_size.height);
+			      window->geometry.width,
+			      window->geometry.height);
 		wl_surface_set_opaque_region(window->surface, region);
 		wl_region_destroy(region);
 	}