[llvm] [SelectionDAG] Fix result index and vector width in unrollExpandedOp (PR #225886)

[Demetrios Chiuratto Agourakis via llvm-commits]

agourakis82 wrote:

Thanks @topperc and @arsenm for the review! All build and test jobs have passed (the buildkite/libcxx-ci failure appears to be an unrelated infrastructure timeout). Could you please land this when you have a moment?

https://github.com/llvm/llvm-project/pull/225886