ASoC: core: Fix possible NULL pointer dereference

snd_soc_of_parse_card_name() may be called before card->dev has been
set, which results in a kernel panic.

Unable to handle kernel NULL pointer dereference at virtual address 00000210
PC is at snd_soc_of_parse_card_name+0x18/0x54
LR is at snow_probe+0x5c/0xd4

Add an error check in snd_soc_of_parse_card_name() to take care of this
case and print out a message in case of error.

Signed-off-by: Tushar Behera <tushar.b@samsung.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

sound/soc/soc-core.c

@@ -4420,9 +4420,16 @@ EXPORT_SYMBOL_GPL(snd_soc_unregister_codec);
 int snd_soc_of_parse_card_name(struct snd_soc_card *card,
 			       const char *propname)
 {
-	struct device_node *np = card->dev->of_node;
+	struct device_node *np;
 	int ret;
 
+	if (!card->dev) {
+		pr_err("card->dev is not set before calling %s\n", __func__);
+		return -EINVAL;
+	}
+
+	np = card->dev->of_node;
+
 	ret = of_property_read_string_index(np, propname, 0, &card->name);
 	/*
 	 * EINVAL means the property does not exist. This is fine providing