ALSA: vmaster: Add snd_ctl_add_followers() helper

Add a new helper to add multiple vmaster followers in a shot. The
same function was open-coded in various places, and this helper
replaces them.

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Takashi Iwai <[e-mail]>

include/sound/control.h

···
 	return _snd_ctl_add_follower(master, follower, 0);
 }
 
+int snd_ctl_add_followers(struct snd_card *card, struct snd_kcontrol *master,
+			  const char * const *list);
+
 /**
  * snd_ctl_add_follower_uncached - Add a virtual follower control
  * @master: vmaster element

sound/core/vmaster.c

···
 }
 EXPORT_SYMBOL(_snd_ctl_add_follower);
 
+/**
+ * snd_ctl_add_followers - add multiple followers to vmaster
+ * @card: card instance
+ * @master: the target vmaster kcontrol object
+ * @list: NULL-terminated list of name strings of followers to be added
+ *
+ * Adds the multiple follower kcontrols with the given names.
+ * Returns 0 for success or a negative error code.
+ */
+int snd_ctl_add_followers(struct snd_card *card, struct snd_kcontrol *master,
+			  const char * const *list)
+{
+	struct snd_kcontrol *follower;
+	int err;
+
+	for (; *list; list++) {
+		follower = snd_ctl_find_id_mixer(card, *list);
+		if (follower) {
+			err = snd_ctl_add_follower(master, follower);
+			if (err < 0)
+				return err;
+		}
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(snd_ctl_add_followers);
+
 /*
  * ctl callbacks for master controls
  */