ASoC: SOF: compress: fix null check after dereference

"cstream" is dereferenced but null checked later. Swap their
positions to avoid potential null dereference.

Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Reviewed-by: Daniel Baluta <daniel.baluta@nxp.com>
Reviewed-by: Péter Ujfalusi <peter.ujfalusi@linux.intel.com>
Signed-off-by: Weiguo Li <liwg06@foxmail.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20220310171651.249385-3-pierre-louis.bossart@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: liwg06

sound/soc/sof/compress.c

@@ -46,15 +46,17 @@ void snd_sof_compr_init_elapsed_work(struct work_struct *work)
  */
 void snd_sof_compr_fragment_elapsed(struct snd_compr_stream *cstream)
 {
-	struct snd_soc_pcm_runtime *rtd = cstream->private_data;
-	struct snd_compr_runtime *crtd = cstream->runtime;
+	struct snd_soc_pcm_runtime *rtd;
+	struct snd_compr_runtime *crtd;
 	struct snd_soc_component *component;
 	struct snd_compr_tstamp *tstamp;
 	struct snd_sof_pcm *spcm;
 
 	if (!cstream)
 		return;
 
+	rtd = cstream->private_data;
+	crtd = cstream->runtime;
 	tstamp = crtd->private_data;
 	component = snd_soc_rtdcom_lookup(rtd, SOF_AUDIO_PCM_DRV_NAME);