output/fifo: make variables more local

src/output/plugins/FifoOutputPlugin.cxx

@@ -260,14 +260,13 @@ fifo_output_play(AudioOutput *ao, const void *chunk, size_t size,
 		 Error &error)
 {
 	FifoOutput *fd = (FifoOutput *)ao;
-	ssize_t bytes;
 
 	if (!fd->timer->IsStarted())
 		fd->timer->Start();
 	fd->timer->Add(size);
 
 	while (true) {
-		bytes = write(fd->output, chunk, size);
+		ssize_t bytes = write(fd->output, chunk, size);
 		if (bytes > 0)
 			return (size_t)bytes;