wayland/egl-stream: Cache texture snippet

While it's not very relevant now, as we would rarely create it anyway
since the buffer nor texture never changes for a surface, it will be in
the future, as the actor state (including its content,
MetaShapedTexture) will be synchronized by the MetaWaylandActorSurface
at a later point in time, and not by MetaWaylandSurface, at state
application time.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/961

src/wayland/meta-wayland-buffer.c

@@ -489,7 +489,7 @@ meta_wayland_buffer_create_snippet (MetaWaylandBuffer *buffer)
   if (!buffer->egl_stream.stream)
     return NULL;
 
-  return meta_wayland_egl_stream_create_snippet ();
+  return meta_wayland_egl_stream_create_snippet (buffer->egl_stream.stream);
 #else
   return NULL;
 #endif /* HAVE_WAYLAND_EGLSTREAM */