ASoC: soc-pcm: add error log

cppcheck warning:

sound/soc/soc-pcm.c:1907:6: style: Variable 'err' is assigned a value
that is never used. [unreadVariable]
 err = dpcm_be_dai_hw_free(fe, stream);
     ^

it's not clear why dpcm_be_dai_hw_free() is sometimes called without
testing the error status, and sometimes an error message is provided.

When in doubt, add an error message for consistency. This may have to
be revisited.
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20210218221921.88991-5-pierre-louis.bossart@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/soc-pcm.c

@@ -1907,6 +1907,8 @@ static int dpcm_fe_dai_hw_free(struct snd_pcm_substream *substream)
 	/* only hw_params backends that are either sinks or sources
 	 * to this frontend DAI */
 	err = dpcm_be_dai_hw_free(fe, stream);
+	if (err < 0)
+		dev_err(fe->dev, "ASoC: hw_free BE failed %d\n", err);
 
 	fe->dpcm[stream].state = SND_SOC_DPCM_STATE_HW_FREE;
 	dpcm_set_fe_update_state(fe, stream, SND_SOC_DPCM_UPDATE_NO);