ASoC: wm_adsp: Check for buffer in trigger stop

Trigger stop can be called in situations where trigger start failed
and as such it can't be assumed the buffer is already attached to
the compressed stream or a NULL pointer may be dereferenced.

Fixes: 639e5eb3 ("ASoC: wm_adsp: Correct handling of compressed streams that restart")
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/wm_adsp.c

@@ -3587,7 +3587,8 @@ int wm_adsp_compr_trigger(struct snd_compr_stream *stream, int cmd)
 		}
 		break;
 	case SNDRV_PCM_TRIGGER_STOP:
-		wm_adsp_buffer_clear(compr->buf);
+		if (wm_adsp_compr_attached(compr))
+			wm_adsp_buffer_clear(compr->buf);
 		break;
 	default:
 		ret = -EINVAL;