mesa/main: clean up invalid pname-check

The logic is a bit easier to follow if we list the cases where this is
supported, rather than the cases where it isn't.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35097>
1 file changed