[InstCombine] clean up foldVectorBinop(); NFC

1. Fix include ordering.
2. Improve variable name (width is bitwidth not number-of-elements).
3. Add local Opcode variable to reduce code duplication.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@343694 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed