radv: do not store meta shaders to the default shader disk cache

radv: do not store meta shaders to the default shader disk cache

Meta shaders are already stored in a different shader cache file.
Storing them in two places wastes disk space and they are never
loaded from the default shader disk cache anyways.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhhuizen <bas@basnieuwenhuizen.nl>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12937>