usb-device-midi: Keep the built-in driver in midi_example.py.

The example prints to console, so no reason not to do this similar to the
other examples.

Tested Windows 10, Linux.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

micropython/usb/examples/device/midi_example.py

@@ -25,7 +25,8 @@ class MIDIExample(MIDIInterface):
 
 
 m = MIDIExample()
-usb.device.get().init(m)
+# Remove builtin_driver=True if you don't want the MicroPython serial REPL available.
+usb.device.get().init(m, builtin_driver=True)
 
 print("Waiting for USB host to configure the interface...")