ALSA: bcd2000: Use guard() for mutex locks

Replace the manual mutex lock/unlock pairs with guard() for code
simplification.

Only code refactoring, and no behavior change.

Signed-off-by: Takashi Iwai <[e-mail]>
Link: https://patch.msgid.link/[e-mail]

sound/usb/bcd2000/bcd2000.c

···
 	char usb_path[32];
 	int err;
 
-	mutex_lock(&devices_mutex);
+	guard(mutex)(&devices_mutex);
 
 	for (card_index = 0; card_index < SNDRV_CARDS; ++card_index)
 		if (!test_bit(card_index, devices_used))
 			break;
 
-	if (card_index >= SNDRV_CARDS) {
-		mutex_unlock(&devices_mutex);
+	if (card_index >= SNDRV_CARDS)
 		return -ENOENT;
-	}
 
 	err = snd_card_new(&interface->dev, index[card_index], id[card_index],
 			THIS_MODULE, sizeof(*bcd2k), &card);
-	if (err < 0) {
-		mutex_unlock(&devices_mutex);
+	if (err < 0)
 		return err;
-	}
 
 	bcd2k = card->private_data;
 	bcd2k->dev = interface_to_usbdev(interface);
···
 	usb_set_intfdata(interface, bcd2k);
 	set_bit(card_index, devices_used);
 
-	mutex_unlock(&devices_mutex);
 	return 0;
 
 probe_error:
 	dev_info(&bcd2k->dev->dev, PREFIX "error during probing");
 	bcd2000_free_usb_related_resources(bcd2k, interface);
 	snd_card_free(card);
-	mutex_unlock(&devices_mutex);
 	return err;
 }
 
···
 	if (!bcd2k)
 		return;
 
-	mutex_lock(&devices_mutex);
+	guard(mutex)(&devices_mutex);
 
 	/* make sure that userspace cannot create new requests */
 	snd_card_disconnect(bcd2k->card);
···
 	clear_bit(bcd2k->card_index, devices_used);
 
 	snd_card_free_when_closed(bcd2k->card);
-
-	mutex_unlock(&devices_mutex);
 }
 
 static struct usb_driver bcd2000_driver = {