ASoC: rt5677-spi: fixup compile warning

ASoC: rt5677-spi: fixup compile warning

This patch fixup this warning

LINUX/sound/soc/codecs/rt5677-spi.c: In function ‘rt5677_spi_pcm_close’:
LINUX/sound/soc/codecs/rt5677-spi.c:114:30: warning: unused variable ‘rtd’ [-Wunused-variable]
  struct snd_soc_pcm_runtime *rtd = substream->private_data;
                              ^~~

Fixes: a0e0d135427c ("ASoC: rt5677: Add a PCM device for streaming hotword via SPI")
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87a79idajh.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>