ASoC: Constify snd_soc_dai_ops variables

The snd_soc_dai_ops variables are not modified after initialization in
these drivers, so make them const.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
diff --git a/sound/soc/codecs/rt5645.c b/sound/soc/codecs/rt5645.c
index 9ce311e..7c59326 100644
--- a/sound/soc/codecs/rt5645.c
+++ b/sound/soc/codecs/rt5645.c
@@ -3110,7 +3110,7 @@
 #define RT5645_FORMATS (SNDRV_PCM_FMTBIT_S16_LE | SNDRV_PCM_FMTBIT_S20_3LE | \
 			SNDRV_PCM_FMTBIT_S24_LE | SNDRV_PCM_FMTBIT_S8)
 
-static struct snd_soc_dai_ops rt5645_aif_dai_ops = {
+static const struct snd_soc_dai_ops rt5645_aif_dai_ops = {
 	.hw_params = rt5645_hw_params,
 	.set_fmt = rt5645_set_dai_fmt,
 	.set_sysclk = rt5645_set_dai_sysclk,