Clear up some more compile warnings

Marlin/src/gcode/lcd/M300.cpp

@@ -37,7 +37,7 @@ void GcodeSuite::M300() {
   uint16_t duration = parser.ushortval('P', 1000);
 
   // Limits the tone duration to 0-5 seconds.
-  NOMORE(duration, 5000);
+  NOMORE(duration, 5000U);
 
   BUZZ(duration, frequency);
 }