arm: Fix typos in comments

The width register has been set to clz(w)-24, not the other way
around. And the 32 bit prep function has got the h parameter in
r4, not in r5.
21 jobs for master in 6 minutes and 6 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Style
passed #268965
amd64 debian
style-check

00:00:23

 
  Build
passed #268966
amd64 debian
build-debian

00:00:41

passed #268974
debian aarch64
build-debian-aarch64

00:01:33

passed #268975
debian aarch64
build-debian-aarch64-clang-5

00:01:05

passed #268978
debian armv7
build-debian-armv7

00:01:42

passed #268979
debian armv7
build-debian-armv7-clang-5

00:01:20

passed #268967
amd64 debian
build-debian-static

00:00:41

passed #268977
debian aarch64
build-debian-werror

00:00:35

passed #268968
amd64 debian
build-debian32

00:00:39

passed #268976
macos
build-macos

00:00:37

passed #268980
amd64 debian allowed to fail
build-ubuntu-snap

00:01:02

passed #268972
amd64 debian
build-win-arm32

00:00:33

passed #268973
amd64 debian
build-win-arm64

00:00:34

passed #268969
amd64 debian
build-win32

00:00:42

passed #268970
amd64 debian
build-win32-unaligned-stack

00:00:46

passed #268971
amd64 debian
build-win64

00:00:47

 
  Test
passed #268981
amd64 debian
test-debian

00:00:49

passed #268982
amd64 debian
test-debian-asan

00:02:20

passed #268983
amd64 debian
test-debian-msan

00:01:06

passed #268984
amd64 debian
test-debian-ubsan

00:01:31

passed #268985
amd64 debian
test-win64

00:00:58