ASoC: txx9: Remove unused rtd variable

Commit a857e073 ("ASoC: txx9: txx9aclc: remove snd_pcm_ops") removed
the last use of the rtd variable but didn't remove its definition,
leading to the following warning/error for MIPS rbtx49xx_defconfig
builds:

sound/soc/txx9/txx9aclc.c: In function 'txx9aclc_pcm_hw_params':
sound/soc/txx9/txx9aclc.c:54:30: error: unused variable 'rtd'
    [-Werror=unused-variable]
  struct snd_soc_pcm_runtime *rtd = snd_pcm_substream_chip(substream);
                              ^~~

Resolve this by removing the unused variable.
Signed-off-by: Paul Burton <paulburton@kernel.org>
Fixes: a857e073 ("ASoC: txx9: txx9aclc: remove snd_pcm_ops")
Cc: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Liam Girdwood <lgirdwood@gmail.com>
Cc: Jaroslav Kysela <perex@perex.cz>
Cc: Takashi Iwai <tiwai@suse.com>
Cc: alsa-devel@alsa-project.org
Link: https://lore.kernel.org/r/20200109191422.334516-1-paulburton@kernel.orgSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/txx9/txx9aclc.c

@@ -51,7 +51,6 @@ static int txx9aclc_pcm_hw_params(struct snd_soc_component *component,
 				  struct snd_pcm_substream *substream,
 				  struct snd_pcm_hw_params *params)
 {
-	struct snd_soc_pcm_runtime *rtd = snd_pcm_substream_chip(substream);
 	struct snd_pcm_runtime *runtime = substream->runtime;
 	struct txx9aclc_dmadata *dmadata = runtime->private_data;