Add cast for string passed into strlen

cores/arduino/USB/USBCore.cpp

@@ -92,7 +92,7 @@ bool USBDeviceClass::sendStringDescriptor(const uint8_t *string, uint8_t maxlen)
 
 	uint8_t buffer[maxlen];
 	buffer[0] = 0x03;
-	buffer[1] = strlen(string) * 2 + 2;
+	buffer[1] = strlen((const char*)string) * 2 + 2;
 
 	uint8_t i;
 	for (i = 2; i < maxlen && *string; i++) {