[llvm] [IR] Fix vector.splice verifier scaling by vscale for fixed length vectors (PR #170807)

[Nikita Popov via llvm-commits]

nikic wrote:

As you are planning to extend this to dynamic indices, the verifier check must be dropped at that point anyway (with poison semantics for the actual runtime value), so we can just defer this until then... (We can't have verifier checks only for the constant case.)

https://github.com/llvm/llvm-project/pull/170807