[X86][SSE] Reuse zeroable element mask in lowerVectorShuffleAsBlend. NFCI

Don't regenerate a zeroable element mask with computeZeroableShuffleElements when its already available.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@286045 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed