[llvm] [AArch64] Fix range check for STGPostIndex (PR #117146)

[David Green via llvm-commits]

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

LGTM.

It might be good if AArch64InstrInfo::verifyInstruction (or something more automatic) could check the ranges of immediates like this too.

https://github.com/llvm/llvm-project/pull/117146