etnaviv: Use the util_pack_color_union() helper.

This snuck in since I cleaned up the other instances of it.

Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5728>
1 file changed