[llvm] [POWERPC] Fixes an error in the handling of the MTVSRBMI instruction for big-endian (PR #151565)

[Amy Kwan via llvm-commits]

amy-kwan wrote:

As https://github.com/llvm/llvm-project/commit/45909ec469cea4bc479d5c7d0731dec8e8e91112 is also in the LLVM 21.x branch, we should probably cherry-pick this fix, too.



https://github.com/llvm/llvm-project/pull/151565