ASoC: Make struct snd_soc_card's dapm_widgets and dapm_routes const

Those should not be modified (and are not) by the core code, so make them const.
This also makes them consistent with the same members of snd_soc_codec.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

include/sound/soc.h

@@ -755,9 +755,9 @@ struct snd_soc_card {
 	/*
 	 * Card-specific routes and widgets.
 	 */
-	struct snd_soc_dapm_widget *dapm_widgets;
+	const struct snd_soc_dapm_widget *dapm_widgets;
 	int num_dapm_widgets;
-	struct snd_soc_dapm_route *dapm_routes;
+	const struct snd_soc_dapm_route *dapm_routes;
 	int num_dapm_routes;
 
 	struct work_struct deferred_resume_work;