mesa: don't reset SamplersValidated if nothing changed

This could prevent error detection, if a uniform change sets
SamplersValidated to true without calling _mesa_update_shader_textures_used.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13416>
1 file changed