NFC: fix possible resource leak

Put the device to avoid resource leak on path that the polling flag is
invalid.

Fixes: a831b913 ("NFC: Do not return EBUSY when stopping a poll that's already stopped")
Signed-off-by: Pan Bian <bianpan2016@163.com>
Link: https://lore.kernel.org/r/20210121153745.122184-1-bianpan2016@163.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/nfc/netlink.c

@@ -852,6 +852,7 @@ static int nfc_genl_stop_poll(struct sk_buff *skb, struct genl_info *info)
 
 	if (!dev->polling) {
 		device_unlock(&dev->dev);
+		nfc_put_device(dev);
 		return -EINVAL;
 	}