ozone/wayland: Fix the 'declaration changes meaning' gcc error

Building the Chrome browser configured to engage the Ozone/Wayland
as its backend by using the gcc compiler collection is failed due
to the 'declaration changes meaning' compile-time error.

This CL fixes the error and gets the sources compiled by both
modern compilers - clang and gcc.

Bug: 1073877
Change-Id: Ib6e480e9b3d1b9dfc3640909b2b3dd1c78cdb7da
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2162865Reviewed-by: Maksim Sisov <msisov@igalia.com>
Reviewed-by: Robert Kroeger <rjkroege@chromium.org>
Commit-Queue: Robert Kroeger <rjkroege@chromium.org>
Cr-Commit-Position: refs/heads/master@{#762037}

ui/ozone/platform/wayland/host/xdg_surface_wrapper_impl.h

@@ -68,7 +68,7 @@ class XDGSurfaceWrapperImpl : public ShellSurfaceWrapper {
   static void CloseTopLevelV6(void* data,
                               struct zxdg_toplevel_v6* zxdg_toplevel_v6);
 
-  xdg_surface* xdg_surface() const;
+  struct xdg_surface* xdg_surface() const;
   zxdg_surface_v6* zxdg_surface() const;
 
  private: