ASoC: dapm: Reset dapm wcache after freeing damp widgets

If there is anything in damp->path_source_cache or
damp->path_sink_cache, it can not be valid after the widgets have been
freed. Without this patch a repeated remove and load of a machine
driver may cause NULL pointer reference in dapm_wcache_lookup() when a
freed widget, not belonging to any list, is haunting in the wcache.

Signed-off-by: Jyri Sarha <jsarha@ti.com>
Reported-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
diff --git a/include/sound/soc-dapm.h b/include/sound/soc-dapm.h
index 7855cfe..95a937e 100644
--- a/include/sound/soc-dapm.h
+++ b/include/sound/soc-dapm.h
@@ -398,6 +398,7 @@
 int snd_soc_dapm_weak_routes(struct snd_soc_dapm_context *dapm,
 			     const struct snd_soc_dapm_route *route, int num);
 void snd_soc_dapm_free_widget(struct snd_soc_dapm_widget *w);
+void snd_soc_dapm_reset_cache(struct snd_soc_dapm_context *dapm);
 
 /* dapm events */
 void snd_soc_dapm_stream_event(struct snd_soc_pcm_runtime *rtd, int stream,