[HID] Added missing return in HID.begin()

Author: cmaglie

hardware/arduino/avr/libraries/HID/HID.cpp

@@ -152,6 +152,7 @@ HID_::HID_(void)
 
 int HID_::begin(void)
 {
+	return 0;
 }
 
 #endif /* if defined(USBCON) */