The format enum space isn't necessarily contiguous so we can't assume
that if it's in the table it's valid. We need to check something.
Fixes: ed6e586562 "intel: properly constify isl_format_layouts"
Reviewed-by: Adam Jackson <ajax@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11191>