(Take 2) Fix oob index in sparse example

[ericcanton]

Re-making this PR commit after updating my Google CLA and GitHub email settings to make this commit using the email address I signed with.

From my other PR:

A sparse matrix with shape [4, 10] is being assigned an element at location [7, 0]. This changes that to the valid [3, 0].

Thanks for your time.

[github-actions[bot]]

Preview

Preview and run these notebook edits with Google Colab:

• site/en/guide/sparse_tensor.ipynb

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Format and style

Use the TensorFlow docs notebook tools to format for consistent source diffs and lint for style:

$ python3 -m pip install -U --user git+https://github.com/tensorflow/docs

$ python3 -m tensorflow_docs.tools.nbfmt notebook.ipynb

$ python3 -m tensorflow_docs.tools.nblint --arg=repo:tensorflow/docs notebook.ipynb

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