freedreno/a6xx: Silence compiler warnings

util_format_compose_swizzles() expects 'const unsigned char' and we
are feeding it 'char'.
24 jobs for !325 with fd/silence-warnings in 49 minutes and 32 seconds (queued for 3 seconds)
detached
Status Job ID Name Coverage
  Build+Test
passed #139083
build:make-gallium-drivers-other

00:09:41

passed #139082
build:make-gallium-drivers-radeonsi

00:06:54

passed #139081
build:make-gallium-drivers-swr

00:12:10

passed #139084
build:make-gallium-st-clover-llvm-39

00:05:59

passed #139085
build:make-gallium-st-clover-llvm-4

00:06:09

passed #139086
build:make-gallium-st-clover-llvm-5

00:05:33

passed #139087
build:make-gallium-st-clover-llvm-6

00:05:37

passed #139088
build:make-gallium-st-clover-llvm-7

00:06:29

passed #139089
build:make-gallium-st-other

00:07:00

passed #139080
build:make-loader-classic-dri

00:10:35

passed #139079
build:make-vulkan

00:06:18

passed #139075
build:meson-gallium-clover-llvm5

00:05:45

passed #139076
build:meson-gallium-clover-llvm6

00:05:39

passed #139077
build:meson-gallium-clover-llvm7

00:04:30

passed #139074
build:meson-gallium-drivers-other

00:07:21

passed #139073
build:meson-gallium-radeonsi

00:03:56

passed #139078
build:meson-gallium-st-other

00:02:21

passed #139072
build:meson-gallium-swr

00:09:14

passed #139071
build:meson-glvnd

00:05:56

passed #139070
build:meson-loader-classic-dri

00:06:12

passed #139069
build:meson-vulkan

00:03:42

passed #139091
build:scons-llvm

00:05:07

passed #139090
build:scons-nollvm

00:05:00

passed #139092
build:scons-swr

00:07:14