midi_inoutdemo.py typo fix. #3

Author: Kevin J Walters

examples/midi_inoutdemo.py

@@ -40,7 +40,7 @@
         # For any other known event just forward it
         if isinstance(msg_in, NoteOn) and msg_in.velocity != 0:
             print("Playing major chord with root", msg_in.note,
-                  "from channel", msg.channel + 1)
+                  "from channel", msg_in.channel + 1)
             for offset in major_chord:
                 new_note = msg_in.note + offset
                 if 0 <= new_note <= 127: