Only pass i2c backend to rtc class

ds3231/main.cpp

@@ -147,7 +147,7 @@ static inline rtc::DateTime receiveTime()
 int main()
 {
 	uart_t serial;
-	rtc::DS3231<i2c::I2c<i2c::Hardware<100'000>>, false> ds3231;
+	rtc::DS3231<i2c::Hardware<100'000>, false> ds3231;
 
 	ds3231.init();
 	serial.init();