[LV] Use buildScalarSteps to also handle VF = 1. (NFCI)

[LV] Use buildScalarSteps to also handle VF = 1. (NFCI)

The code in buildScalarSteps already properly handles creating the
scalar induction values with VF = 1. Use it directly instead of using
extra code to handle that case.

Suggested by @Ayal in D133760.