radv: Deal with unused attachments in mip flush

Fixes: 4cce4d22a72 ("radv: Fix a hang on CB change by adding flushes.")
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7813>
(cherry picked from commit aed8d30b507568b7fc0f32afca012f8def5aca16)
2 files changed