Tools: Audio: Test: In Matlab tests by default put trace to /dev/null

The trace print slows down the test a lot while the testbench
trace output is not needed usually in these audio quality
tests. The test script can set .trace to redirect trace to a file
that is also a lot faster than scrolling the trace in Matlab
or Octave shell.

Signed-off-by: Seppo Ingalsuo <seppo.ingalsuo@linux.intel.com>

tools/test/audio/test_utils/test_run.m

@@ -82,6 +82,8 @@ end
 
 if isfield(test, 'trace')
 	fprintf(fh, 'FN_TRACE=\"%s\"\n', test.trace);
+else
+	fprintf(fh, 'FN_TRACE=\"/dev/null"\n');
 end
 
 % Override defaults in comp_run.sh