[InstCombine] use more specific pattern matchers; NFCI

Follow-up from r274465: we don't need to capture the value in these cases, 
so just match the constant that we're looking for. m_One/m_Zero work with
vector splats as well as scalars.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@274670 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed