[SVE] Remove calls to VectorType::getNumElements from Instrumentation

Reviewers: efriedma, pcc, gchatelet, kmclaughlin, sdesmalen

Reviewed By: sdesmalen

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D82241