ASoC: rk3399_gru_sound: Fix non static symbol warning

Fixes the following sparse warning:

sound/soc/rockchip/rk3399_gru_sound.c:41:14: warning:
 symbol 'rt5514_dmic_delay' was not declared. Should it be static?
Signed-off-by: NWei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: NMark Brown <broonie@kernel.org>

sound/soc/rockchip/rk3399_gru_sound.c

@@ -38,7 +38,7 @@
 
 #define SOUND_FS	256
 
-unsigned int rt5514_dmic_delay;
+static unsigned int rt5514_dmic_delay;
 
 static struct snd_soc_jack rockchip_sound_jack;