[X86][SSE] Don't duplicate Lower256IntArith functionality in LowerMul. NFC.

LowerMul v32i8 on AVX2 needs to split the 256-bit sources to allow sign-extension back to v16i16 to occur. Since this is basically the same as Lower256IntArith we simplify by using that here instead.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@264506 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed