[AFSK] Fixed sign

examples/AFSK/AFSK_Imperial_March/AFSK_Imperial_March.ino

@@ -70,7 +70,7 @@ void loop() {
   int wholenote = (60000 * 4) / 120;
 
   // iterate over the melody
-  for(int note = 0; note < sizeof(melody) / sizeof(melody[0]); note += 2) {
+  for(unsigned int note = 0; note < sizeof(melody) / sizeof(melody[0]); note += 2) {
     // calculate the duration of each note
     int noteDuration = 0;
     int divider = melody[note + 1];