[media] rc-core: Initialize return value to zero

At ir_setkeycode, if INPUT_KEYMAP_BY_INDEX is used, the routine may return
an invalid value if not error.
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/rc/rc-main.c

@@ -325,7 +325,7 @@ static int ir_setkeycode(struct input_dev *idev,
 	struct rc_map *rc_map = &rdev->rc_map;
 	unsigned int index;
 	unsigned int scancode;
-	int retval;
+	int retval = 0;
 	unsigned long flags;
 
 	spin_lock_irqsave(&rc_map->lock, flags);