extcon: Remove potential problem when calling extcon_register_notifier()

This patch removes the potential problem of extcon_register_notifier()
when edev parameter is NULL. When edev is NULL, this function returns
the first extcon device which includes the sepecific external connector
of second paramter. But, it don't guarantee the same operation in all cases.
To remove this confusion and potential problem, this patch fixes it.
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>

drivers/extcon/extcon.c

@@ -906,35 +906,16 @@ int extcon_register_notifier(struct extcon_dev *edev, unsigned int id,
 	unsigned long flags;
 	int ret, idx = -EINVAL;
 
-	if (!nb)
+	if (!edev || !nb)
 		return -EINVAL;
 
-	if (edev) {
-		idx = find_cable_index_by_id(edev, id);
-		if (idx < 0)
-			return idx;
-
-		spin_lock_irqsave(&edev->lock, flags);
-		ret = raw_notifier_chain_register(&edev->nh[idx], nb);
-		spin_unlock_irqrestore(&edev->lock, flags);
-	} else {
-		struct extcon_dev *extd;
-
-		mutex_lock(&extcon_dev_list_lock);
-		list_for_each_entry(extd, &extcon_dev_list, entry) {
-			idx = find_cable_index_by_id(extd, id);
-			if (idx >= 0)
-				break;
-		}
-		mutex_unlock(&extcon_dev_list_lock);
+	idx = find_cable_index_by_id(edev, id);
+	if (idx < 0)
+		return idx;
 
-		if (idx >= 0) {
-			edev = extd;
-			return extcon_register_notifier(extd, id, nb);
-		} else {
-			ret = -ENODEV;
-		}
-	}
+	spin_lock_irqsave(&edev->lock, flags);
+	ret = raw_notifier_chain_register(&edev->nh[idx], nb);
+	spin_unlock_irqrestore(&edev->lock, flags);
 
 	return ret;
 }