scene/surfaceitem_wayland: immediately update the release point of the texture
The texture's buffer and release point will be changed before the next time it's accessed, so keeping the old release point referenced just unnecessarily keeps a buffer from being re-used by the client.
This works around some freezes in Chromium, which doesn't deal well with buffers being kept referenced by KWin after it sets a different one on the surface.
I want to change the API a bit more to make this issue harder to trigger, but for 6.7 this is better.