Fix compiler warnings.

../lib/Target/X86/X86ISelLowering.cpp:9715:7: error: unused variable 'OpVT' [-Werror,-Wunused-variable]
  EVT OpVT = Op0.getValueType();
      ^
../lib/Target/X86/X86ISelLowering.cpp:9763:14: error: unused variable 'NumElems' [-Werror,-Wunused-variable]
    unsigned NumElems = VT.getVectorNumElements();