[llvm] [LV][NFC] Remove remaining uses of undef in tests (PR #169357)

[David Sherwood via llvm-commits]

david-arm wrote:

I also realised we weren't actually checking anything in llvm/test/Transforms/LoopVectorize/interleaved-accesses-uniform-load.ll even though it had CHECK lines. I've fixed the test now, which also removes another 'undef'.

https://github.com/llvm/llvm-project/pull/169357