Fix MIDI output endpoint to use the out direction

[nezumee]

Description

Bug: cannot send MIDI messages to keyboard. The callback functions registered via midi_register_* are never invoked. This blocks implementing things like MIDI controller feedback where DAW software sends messages to the controller to turn indicator lights on/off etc.

Fix: update the endpoint direction to match the stream direction for MIDI output in lufa.c. The IN/OUT mismatch was introduced in f209f91, likely a copypaste error.

Note that I don't actually understand how this works :), the fix came from reviewing code and applying common sense. I did validate in a custom keyboard that this change unblocks sending MIDI notes to the keyboard and receiving them via midi_register_noteon_callback.

Types of Changes

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

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• 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.
• 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).

[nezumee]

First time making a PR here, please say if I'm doing anything wrong.

This is a small fix for what's likely a rarely used feature (based on the state of the docs). I think it can be useful though, in case people want to make MIDI controllers based on QMK.

[keyboard-magpie]

A very tidy first PR, well found.