[llvm] [LV] Fix narrow-interleave with broadcast. (PR #148572)

[David Green via llvm-commits]

davemgreen wrote:

See the comment on https://github.com/llvm/llvm-project/commit/2787759ef2e41b19f8bfde06fe9a26b25d1f5834 about this currently making things worse as written.

https://github.com/llvm/llvm-project/pull/148572