ASoC: Intel: Atom: platform-pcm: remove redundant assignment

fix cppcheck warning:

sound/soc/intel/atom/sst-mfld-platform-pcm.c:387:9: warning: Identical
condition and return expression 'ret_val', return value is always 0
[identicalConditionAfterEarlyExit]
 return ret_val;
        ^

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200813200147.61990-4-pierre-louis.bossart@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/intel/atom/sst-mfld-platform-pcm.c

@@ -366,7 +366,7 @@ static int sst_media_prepare(struct snd_pcm_substream *substream,
 		struct snd_soc_dai *dai)
 {
 	struct sst_runtime_stream *stream;
-	int ret_val = 0, str_id;
+	int ret_val, str_id;
 
 	stream = substream->runtime->private_data;
 	str_id = stream->stream_info.str_id;