radv: Use correct border swizzle on GFX9+.
We only need the format swizzle, not the full swizzle. Fixes: 57e796a1 ("radv: Implement VK_EXT_custom_border_color") Gitlab: mesa/mesa#4020 Reviewed-by:Samuel Pitoiset <samuel.pitoiset@gmail.com> Part-of: <mesa/mesa!9731>