ASoC: dapm: Make sure we have a card when displaying component widgets

BugLink: http://bugs.launchpad.net/bugs/1578798

commit 47325078 upstream.

The dummy component is reused for all cards so we special case and don't
bind it to any of them.  This means that code like that displaying the
component widgets that tries to look at the card will crash.  In the
future we will fix this by ensuring that the dummy component looks like
other components but that is invasive and so not suitable for a fix.
Instead add a special case check here.
Reported-by: Harry Pan <harry.pan@intel.com>
Suggested-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

sound/soc/soc-dapm.c

@@ -2188,6 +2188,13 @@ static ssize_t dapm_widget_show_component(struct snd_soc_component *cmpnt,
 	int count = 0;
 	char *state = "not set";
 
+	/* card won't be set for the dummy component, as a spot fix
+	 * we're checking for that case specifically here but in future
+	 * we will ensure that the dummy component looks like others.
+	 */
+	if (!cmpnt->card)
+		return 0;
+
 	list_for_each_entry(w, &cmpnt->card->widgets, list) {
 		if (w->dapm != dapm)
 			continue;