readBytesUntil from configured UARTDevice instead of Serial

[andreanielsen83]

Reading lines from the P1 port using

          int len = Serial.readBytesUntil('\n', buffer, BUF_SIZE);

appears to be hardcoded to reading from RX instead of the configured rx_pin

uart:
  id: uart_bus
  rx_pin:
    number: GPIO6
    inverted: true
  baud_rate: 115200

Please note I haven't tested this change on a dev board, so cannot claim it is generic - but I think it is.

[cadwal]

This is included in the current code.