[DirectX] Fix handling of i8 GEPs in DXILDataScalarization#145780

Icohedron wants to merge 2 commits intollvm:mainllvm/llvm-project:mainfrom

Icohedron:dxil-data-scalarizer-i8-gepsIcohedron/llvm-project:dxil-data-scalarizer-i8-gepsCopy head branch name to clipboard