Update I2C_READ_CONTINUOUSLY to match I2C_READ w/ no provided slaveRegister

If you're feeling ambitious, a good approach would be to start a test file for I2C. You can use the [encoder_test](https://github.com/firmata/arduino/blob/configurable_dev/test/encoder_test/encoder_test.ino) file as an example. Testing like this is really only possible with code in the configurable branch since it's modular.  For now, the only test to add is to ensure that the values in the query struct (query[i].addr, query[i].reg, query[i].bytes) match the expected values when read continuously is set with and without a slave address.

I'll try to find some time to add test files for other Firmata feature classes as well.