ASoC: fsl: Fix unused variable warning

The variable rtd was left unused in psc_dma_free(), even unnoticed
during conversion to a new style:
  sound/soc/fsl/mpc5200_dma.c:342:30: warning: unused variable 'rtd' [-Wunused-variable]

Drop the superfluous one.

Fixes: 6d1048bc ("ASoC: fsl: mpc5200_dma: remove snd_pcm_ops")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20200803144630.9615-1-tiwai@suse.deSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/fsl/mpc5200_dma.c

@@ -339,7 +339,6 @@ static int psc_dma_new(struct snd_soc_component *component,
 static void psc_dma_free(struct snd_soc_component *component,
 			 struct snd_pcm *pcm)
 {
-	struct snd_soc_pcm_runtime *rtd = pcm->private_data;
 	struct snd_pcm_substream *substream;
 	int stream;