ASoC: rsrc-card: remove unused ret

'04700027("ASoC: rsrc-card: cleanup for DPCM")'
cleanuped rsrc-card driver, but then, unused ret was left.
Below warning happen without this patch

${LINUX}/sound/soc/sh/rcar/rsrc-card.c: In function 'rsrc_card_startup':
${LINUX}/sound/soc/sh/rcar/rsrc-card.c:78:6: warning: unused variable \
	'ret' [-Wunused-variable]
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sh/rcar/rsrc-card.c

@@ -75,8 +75,6 @@ static int rsrc_card_startup(struct snd_pcm_substream *substream)
 	struct rsrc_card_priv *priv =	snd_soc_card_get_drvdata(rtd->card);
 	struct rsrc_card_dai *dai_props =
 		rsrc_priv_to_props(priv, rtd - rtd->card->rtd);
-	int ret;
-
 
 	return clk_prepare_enable(dai_props->clk);
 }