ASoC: dapm: Fix potential DAI widget pointer deref when linking DAIs

Sometime a component or topology may configure a DAI widget with no
private data leading to a dev_dbg() dereferencne of this data.

Fix this to check for non NULL private data and let users know if widget
is missing DAI.

Signed-off-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/soc-dapm.c

@@ -4073,6 +4073,13 @@ int snd_soc_dapm_link_dai_widgets(struct snd_soc_card *card)
 			continue;
 		}
 
+		/* let users know there is no DAI to link */
+		if (!dai_w->priv) {
+			dev_dbg(card->dev, "dai widget %s has no DAI\n",
+				dai_w->name);
+			continue;
+		}
+
 		dai = dai_w->priv;
 
 		/* ...find all widgets with the same stream and link them */