Cleanup build warnings (tracker module)

[araujo88]

This is related to #32 . Fixes build warnings for the tracker module.

[bazz1tv]

Thank you so much for making a contribution towards SNES Tracker 🙇‍♂️. Although I am not actively working on the project, I am regaining interest in it steadily. When I resume, I would love to get these pull requests synchronized with the current state of the project.