Fix reference doc variable references

[rolson]

Fix reference doc variable references

This PR fixes the code samples for atomic lazy reference types.

Checklist

• [x] I've read the Contribution Guidelines
• [x] My contributions are licensed under the Swift license.
• [x] I've followed the coding style of the rest of the project.
• [ ] I've added tests covering all new code paths my change adds to the project (if appropriate).
• [ ] I've verified that my change does not break any existing tests.
• [x] I've updated the documentation if necessary.

[lorentey]

@swift-ci test

[rolson]

thank you