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.de


Signed-off-by: Mark Brown <broonie@kernel.org>