[Fix doc example] FSMT

[ydshieh]

What does this PR do?

Fix doc example.

Without this fix, I get the following error

            batch_size = inputs_tensor.shape[0]
          File "/home/yih_dar_huggingface_co/transformers/src/transformers/tokenization_utils_base.py", line 253, in __getattr__
            raise AttributeError
        AttributeError

where inputs_tensor has type BatchEncoding.

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[sgugger]

Thanks for fixing!