Minor constant_op.constant improvement

Before:
entry {
  name: "MicroBenchmarks.benchmark_create_constant"
  iters: 30000
  wall_time: 2.04829374949
  extras {
    key: "examples_per_sec"
    value {
      double_value: 488211.224708
    }
  }
}

After:
entry {
  name: "MicroBenchmarks.benchmark_create_constant"
  iters: 30000
  wall_time: 1.73307259878
  extras {
    key: "examples_per_sec"
    value {
      double_value: 577009.872931
    }
  }
}
PiperOrigin-RevId: 220667201