[llvm] [AArch64] Fix regression from “Fold scalar-to-vector shuffles into DUP/FMOV" (PR #178227)

[David Green via llvm-commits]

davemgreen wrote:

Is it possible to reduce it to something smaller (that was previously still stuck), and add it as a test case?

https://github.com/llvm/llvm-project/pull/178227