sound: Fix warnings relating to ignored return value in snd_card_register

Do not ignore the return of 'device_create_file' in
'snd_card_register' and thereby fixing the following warnings:

sound/core/init.c: In function 'snd_card_register':
sound/core/init.c:640: warning: ignoring return value of
'device_create_file', declared with attribute warn_unused_result
sound/core/init.c:641: warning: ignoring return value of
'device_create_file', declared with attribute warn_unused_result

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/init.c

@@ -637,8 +637,12 @@ int snd_card_register(struct snd_card *card)
 #endif
 #ifndef CONFIG_SYSFS_DEPRECATED
 	if (card->card_dev) {
-		device_create_file(card->card_dev, &card_id_attrs);
-		device_create_file(card->card_dev, &card_number_attrs);
+		err = device_create_file(card->card_dev, &card_id_attrs);
+		if (err < 0)
+			return err;
+		err = device_create_file(card->card_dev, &card_number_attrs);
+		if (err < 0)
+			return err;
 	}
 #endif
 	return 0;