ps2/avr: use the correct file name

[idank]

This was missed in #14895.

Thanks to fauxpark for spotting this.

Description

Fixes PS2 busywait compilation.

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Checklist

• [ x] My code follows the code style of this project: C, Python
• [ x] I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• [x ] I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).