extcon: remove redundant assignment to variable idx

The variable idx is being initialized with a value that is never read
and it is being updated later with a new value.  The initialization is
redundant and can be removed.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>

drivers/extcon/extcon.c

@@ -900,7 +900,7 @@ int extcon_register_notifier(struct extcon_dev *edev, unsigned int id,
 			     struct notifier_block *nb)
 {
 	unsigned long flags;
-	int ret, idx = -EINVAL;
+	int ret, idx;
 
 	if (!edev || !nb)
 		return -EINVAL;