Fix: consumerd: add missing put_subbuf for ust and kernel errors

While reading a sub-buffer, error handling need to put the sub-buffer,
else all future attempts to use the stream will trigger warnings.

The affects recent features added to UST and kernel tracing.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>