Fix: ret may be used uninitialized in sample_channel_positions()

sample_channel_positions() returns garbage if
cds_lfht_is_node_deleted(&stream->node.node) on first and "possibly"
only iteration of the consumer_data.stream_per_chan_id_ht hash table.

Found by scan-build.

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>