[llvm] [MC][ARM] Fix crash when assembling Thumb 'movs r0, #foo'. (PR #115026)

[Alfie Richards via llvm-commits]

https://github.com/AlfieRichardsArm approved this pull request.

LGTM! The revalidate seems like a good pattern as there's more I can imagine could use this pattern

https://github.com/llvm/llvm-project/pull/115026