Remove chip parameter, it is no longer used inside the driver.
Move the zero-length write check from Tx_Ringbuffer to it950x_tx_write, and return 0 in this case.  Rename any remaining use of Error_NO_ERROR with ModulatorError_NO_ERROR (we don't need two defines for that, and the use of non-Linux error codes needs cleaning up later anyway) and then delete error.h as it is no longer needed.