doc: fix nvs example case sensitivity

[finger563]

Description

Motivation and Context

How has this been tested?

Screenshots (if appropriate, e.g. schematic, board, console logs, lab pictures):

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [x] Documentation Update
• [ ] Hardware (schematic, board, system design) change
• [ ] Software change

Checklist:

• [x] My change requires a change to the documentation.
• [x] I have added / updated the documentation related to this change via either README or WIKI

Software

• [ ] I have added tests to cover my changes.
• [ ] I have updated the .github/workflows/build.yml file to add my new test to the automated cloud build github action.
• [ ] All new and existing tests passed.
• [ ] My code follows the code style of this project.

Hardware

• [ ] I have updated the design files (schematic, board, libraries).
• [ ] I have attached the PDFs of the SCH / BRD to this PR
• [ ] I have updated the design output (GERBER, BOM) files.