[llvm] [VPlan] Improve code in VPWidenIntrinsic (NFC) (PR #141936)

[Florian Hahn via llvm-commits]

https://github.com/fhahn approved this pull request.

LGTM, thanks.

Commit message could be a bit more specific, mentioning using operands()

https://github.com/llvm/llvm-project/pull/141936