AVX: Fix a bug in WidenMaskArithmetic.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171397 91177308-0d34-0410-b5e6-96231b3b80d8
AVX: Fix a bug in WidenMaskArithmetic.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171398 91177308-0d34-0410-b5e6-96231b3b80d8