nir/samplers: don't zero samplers_used/txf.

This allows this pass to be run multiple times and the results are
just or'ed together.

It fixes on test on llvmpipe nir, and regresses none.

Suggested by Kenneth

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
39 jobs for !2911 with st-nir-fix-sampler-lowering in 12 minutes and 51 seconds (queued for 3 seconds)
detached
Status Job ID Name Coverage
  Container
passed #1044518
aarch64
arm_build

00:00:18

passed #1044519
aarch64
arm_test

00:00:30

passed #1044514
lava_arm64

00:00:30

passed #1044513
lava_armhf

00:00:30

passed #1044515
x86_build

00:00:22

passed #1044517
x86_build_old

00:00:19

passed #1044516
x86_test

00:00:22

 
  Build
passed #1044521
lava-build:arm64

00:04:46

passed #1044520
lava-build:armhf

00:04:06

passed #1044525
aarch64
meson-arm64

00:05:33

passed #1044524
aarch64
meson-armhf

00:02:50

passed #1044526
meson-clang

00:10:51

passed #1044529
meson-clover

00:10:43

passed #1044530
meson-clover-old-llvm

00:06:14

passed #1044532
meson-i386

00:05:09

passed #1044523
meson-main

00:11:32

passed #1044533
meson-mingw32-x86_64

00:08:40

passed #1044522
meson-testing

00:04:12

passed #1044531
meson-vulkan

00:03:42

passed #1044534
scons

00:03:02

passed #1044535
scons-old-llvm

00:03:54

passed #1044527
scons-swr

00:11:29

passed #1044528
scons-win64

00:12:26

 
  Test
passed #1044551
db410c
arm64_a306_gles2

00:04:59

passed #1044548
mesa-cheza
arm64_a630_gles2

00:01:32

passed #1044550
mesa-cheza
arm64_a630_gles3

00:06:14

passed #1044549
mesa-cheza
arm64_a630_gles31

00:04:07

passed #1044536
lava-rk3288-veyron-jaq
panfrost-t760-test:armhf

00:06:09

passed #1044537
lava-rk3399-gru-kevin
panfrost-t860-test:arm64

00:05:54

passed #1044539
piglit-glslparser+quick_shader

00:06:03

passed #1044538
piglit-quick_gl

00:05:54

passed #1044540
test-llvmpipe-gles2

00:03:00

passed #1044541
test-softpipe-gles2

00:01:46

passed #1044544
test-softpipe-gles31 1/4

00:03:07

passed #1044542
test-softpipe-gles3 1/2

00:03:57

passed #1044545
test-softpipe-gles31 2/4

00:04:07

passed #1044546
test-softpipe-gles31 3/4

00:04:59

passed #1044547
test-softpipe-gles31 4/4

00:03:34

passed #1044543
test-softpipe-gles3 2/2

00:05:30