Bluetooth: 6LoWPAN: add missing hci_dev_put() in get_l2cap_conn()

hci_get_route() takes reference, we should use hci_dev_put() to release
it when not need anymore.

Fixes: 6b8d4a6a ("Bluetooth: 6LoWPAN: Use connected oriented channel instead of fixed one")
Signed-off-by: Wang ShaoBo <bobo.shaobowang@huawei.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

net/bluetooth/6lowpan.c

@@ -972,6 +972,7 @@ static int get_l2cap_conn(char *buf, bdaddr_t *addr, u8 *addr_type,
 	hci_dev_lock(hdev);
 	hcon = hci_conn_hash_lookup_le(hdev, addr, *addr_type);
 	hci_dev_unlock(hdev);
+	hci_dev_put(hdev);
 
 	if (!hcon)
 		return -ENOENT;