When lowering an inreg sext first shift left, then right arithmetically.

Shifting right two times will only yield zero. Should fix
SingleSource/UnitTests/SignlessTypes/factor.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@172322 91177308-0d34-0410-b5e6-96231b3b80d8