prog_to_nir: fix write from vps to FOG

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>
24 jobs for !328 with fog_nir_fix in 28 minutes and 48 seconds (queued for 2 seconds)
detached
Status Job ID Name Coverage
  Build+Test
passed #139480
build:make-gallium-drivers-other

00:09:40

passed #139479
build:make-gallium-drivers-radeonsi

00:06:28

passed #139478
build:make-gallium-drivers-swr

00:12:09

passed #139481
build:make-gallium-st-clover-llvm-39

00:07:40

passed #139482
build:make-gallium-st-clover-llvm-4

00:07:11

passed #139483
build:make-gallium-st-clover-llvm-5

00:07:46

passed #139484
build:make-gallium-st-clover-llvm-6

00:07:47

passed #139485
build:make-gallium-st-clover-llvm-7

00:09:50

passed #139486
build:make-gallium-st-other

00:05:47

passed #139477
build:make-loader-classic-dri

00:11:15

passed #139476
build:make-vulkan

00:06:34

passed #139472
build:meson-gallium-clover-llvm5

00:05:48

passed #139473
build:meson-gallium-clover-llvm6

00:06:10

passed #139474
build:meson-gallium-clover-llvm7

00:06:13

passed #139471
build:meson-gallium-drivers-other

00:07:39

passed #139470
build:meson-gallium-radeonsi

00:04:16

passed #139475
build:meson-gallium-st-other

00:05:24

passed #139469
build:meson-gallium-swr

00:09:21

passed #139468
build:meson-glvnd

00:05:07

passed #139467
build:meson-loader-classic-dri

00:04:30

passed #139466
build:meson-vulkan

00:02:42

passed #139488
build:scons-llvm

00:04:52

passed #139487
build:scons-nollvm

00:05:04

passed #139489
build:scons-swr

00:07:03