[Matrix] Use FixedVectorType everywhere in LowerMatrixIntrinsics. NFC#142316

jroelofs merged 1 commit intollvm:mainllvm/llvm-project:mainfrom

jroelofs:jroelofs/lower-matrix-fvtjroelofs/llvm-project:jroelofs/lower-matrix-fvtCopy head branch name to clipboard