for fragment programs we already treat fog as a single component value,
but for vp we didn't.
Fixes fog related piglit tests with my out of tree Nouveau nir patches.
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>