perf cs-etm: Allow no CoreSight sink to be specified on command line

Adjust the handling of the session sink selection to allow no sink to be
selected on the command line. This then forwards the sink selection to
the CoreSight infrastructure which will attempt to select a sink based
on the default sink select priorities.
Signed-off-by: NMike Leach <mike.leach@linaro.org>
Tested-by: NLeo Yan <leo.yan@linaro.org>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: coresight@lists.linaro.org
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/arch/arm/util/cs-etm.c

@@ -243,10 +243,10 @@ static int cs_etm_set_sink_attr(struct perf_pmu *pmu,
 	}
 
 	/*
-	 * No sink was provided on the command line - for _now_ treat
-	 * this as an error.
+	 * No sink was provided on the command line - allow the CoreSight
+	 * system to look for a default
 	 */
-	return ret;
+	return 0;
 }
 
 static int cs_etm_recording_options(struct auxtrace_record *itr,