Suspected typo in tmc2209/uartcomm.go

Slave address is fixed at zero in ReadRegister but not in WriteRegister and that seems like a possible problem to me.

I tried to copy the relevant code sections but yikes!  Wrapping it with the <> option didn't look good at all, so just leaving the two lines : 

WriteRegister has 
	comm.address,               // Slave address

ReadRegister has 
	writeBuffer[1] = 0x00            // Slave address
