replace  `FLAGS.batch_size` by `images.get_shape()[0]`
replace  `FLAGS.batch_size` by `images.get_shape()[0]`

We can directly get `batch_size` by `images.get_shape()[0]` in `inference` method, since maybe we will not use `cifar.inputs` method to build the input.
tensorflow/examples,tensorflow/examples,tensorflow/examples,tensorflow/examples,tensorflow/examples,tensorflow/examples,tensorflow/examples,tensorflow/examples,tensorflow/examples