examples: Fix rfnoc_replay_samples_from_file

It was creating a TX streamer with zero channels.

Without this fix, you might see an error like this:

```
Error: AssertionError: channel < _mtu_out.size()
in connect_channel at
/path/to/uhd/host/lib/rfnoc/rfnoc_tx_streamer.cpp:127
```

1 files changed, 2 insertions, 2 deletions

diff --git a/host/examples/rfnoc_replay_samples_from_file.cpp b/host/examples/rfnoc_replay_samples_from_file.cpp
index 2c1e5cb71..ed7742688 100644
--- a/host/examples/rfnoc_replay_samples_from_file.cpp
+++ b/host/examples/rfnoc_replay_samples_from_file.cpp
@@ -147,8 +147,8 @@ int UHD_SAFE_MAIN(int argc, char* argv[])
     uhd::tx_streamer::sptr tx_stream;
     uhd::tx_metadata_t tx_md;
 
-    stream_args.args            = streamer_args;
-    tx_stream = graph->create_tx_streamer(stream_args.channels.size(), stream_args);
+    stream_args.args = streamer_args;
+    tx_stream        = graph->create_tx_streamer(1, stream_args);
     graph->connect(tx_stream, 0, replay_ctrl->get_block_id(), replay_chan);
     graph->commit();