ASoC: SOF: ipc3-dtrace: Return from dtrace_read if there is no new data available

If no new trace data is available then return immediately, there is no
need to continue with the execution of the trace_read() function.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Link: https://lore.kernel.org/r/20220610080119.30880-4-peter.ujfalusi@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sof/ipc3-dtrace.c

@@ -353,6 +353,10 @@ static ssize_t dfsentry_dtrace_read(struct file *file, char __user *buffer,
 		return -EIO;
 	}
 
+	/* no new trace data */
+	if (!avail)
+		return 0;
+
 	/* make sure count is <= avail */
 	if (count > avail)
 		count = avail;