[Bluetooth] Check if DLC is still attached to the TTY

If the DLC device is no longer attached to the TTY device, then it
makes no sense to go through with changing the termios settings.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c
index 5833b87..b8e3a5f 100644
--- a/net/bluetooth/rfcomm/tty.c
+++ b/net/bluetooth/rfcomm/tty.c
@@ -765,6 +765,9 @@
 
 	BT_DBG("tty %p termios %p", tty, old);
 
+	if (!dev)
+		return;
+
 	/* Handle turning off CRTSCTS */
 	if ((old->c_cflag & CRTSCTS) && !(new->c_cflag & CRTSCTS)) 
 		BT_DBG("Turning off CRTSCTS unsupported");