[SVE] Eliminate calls to default-false VectorType::get() from FuzzMutate

Reviewers: efriedma, kmclaughlin, sdesmalen, bogner, chandlerc, c-rhodes, david-arm, fpetrogalli

Reviewed By: c-rhodes

Subscribers: tschuett, hiraditya, rkruppe, psnobl, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D80325