ALSA: hda - Fix the return value if cb func is already registered

If the cb function is already registered, should return the pointer
of the structure hda_jack_callback which contains this cb func, but
instead it returns the NULL.

Now fix it by replacing func_is_already_in_callback_list() with
find_callback_from_list().

Fixes: f4794c6 ("ALSA: hda - Don't register a cb func if it is registered already")
Reported-and-suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Hui Wang <hui.wang@canonical.com>
Link: https://lore.kernel.org/r/20201022030221.22393-1-hui.wang@canonical.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>

Author: jason77-wang

sound/pci/hda/hda_jack.c

@@ -275,16 +275,21 @@ int snd_hda_jack_detect_state_mst(struct hda_codec *codec,
 }
 EXPORT_SYMBOL_GPL(snd_hda_jack_detect_state_mst);
 
-static bool func_is_already_in_callback_list(struct hda_jack_tbl *jack,
-					     hda_jack_callback_fn func)
+static struct hda_jack_callback *
+find_callback_from_list(struct hda_jack_tbl *jack,
+			hda_jack_callback_fn func)
 {
 	struct hda_jack_callback *cb;
 
+	if (!func)
+		return NULL;
+
 	for (cb = jack->callback; cb; cb = cb->next) {
 		if (cb->func == func)
-			return true;
+			return cb;
 	}
-	return false;
+
+	return NULL;
 }
 
 /**
@@ -309,7 +314,10 @@ snd_hda_jack_detect_enable_callback_mst(struct hda_codec *codec, hda_nid_t nid,
 	jack = snd_hda_jack_tbl_new(codec, nid, dev_id);
 	if (!jack)
 		return ERR_PTR(-ENOMEM);
-	if (func && !func_is_already_in_callback_list(jack, func)) {
+
+	callback = find_callback_from_list(jack, func);
+
+	if (func && !callback) {
 		callback = kzalloc(sizeof(*callback), GFP_KERNEL);
 		if (!callback)
 			return ERR_PTR(-ENOMEM);