[Bluetooth] Fix reference count when connection lookup fails

When the connection lookup for the device structure fails, the reference
count for the HCI device needs to be decremented.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c
index 1958ad1..5833b87 100644
--- a/net/bluetooth/rfcomm/tty.c
+++ b/net/bluetooth/rfcomm/tty.c
@@ -172,12 +172,10 @@
 		return NULL;
 
 	conn = hci_conn_hash_lookup_ba(hdev, ACL_LINK, &dev->dst);
-	if (!conn)
-		return NULL;
 
 	hci_dev_put(hdev);
 
-	return &conn->dev;
+	return conn ? &conn->dev : NULL;
 }
 
 static int rfcomm_dev_add(struct rfcomm_dev_req *req, struct rfcomm_dlc *dlc)