gallium/util: Add const to u_range_intersect

This doesn't modify the range, so it can accept a const pointer.
15 jobs for !589 with iris-async in 10 minutes and 12 seconds (queued for 1 second)
latest detached
Status Job ID Name Coverage
  Containers Build
passed #219505
ubuntu

00:00:18

 
  Build+Test
passed #219506
autotools

00:09:51

passed #219508
meson-clang

00:05:19

passed #219514
meson-gallium-clover-llvm

00:03:55

passed #219515
meson-gallium-clover-llvm39

00:02:28

passed #219513
meson-gallium-drivers-other

00:05:51

passed #219512
meson-gallium-radeonsi

00:04:36

passed #219516
meson-gallium-st-other

00:04:00

passed #219507
meson-gallium-swr

00:07:02

passed #219511
meson-glvnd

00:05:01

passed #219510
meson-loader-classic-dri

00:03:50

passed #219509
meson-vulkan

00:01:23

passed #219518
scons-llvm

00:03:56

passed #219517
scons-nollvm

00:03:24

passed #219519
scons-swr

00:07:50