Fix deadlock with Driver::write

Use a spin lock to recheck the queue size until it has room to push.

platform/posix/ftdi.cpp

@@ -199,6 +199,5 @@ void FTDI::writeTask() {
 			continue;
 
 		ftdi.write(writeOp.bytes.data(), (int)writeOp.bytes.size());
-		onWrite();
 	}
 }