Bluetooth: Fix issue with return value of rfcomm_sock_sendmsg()

In case of connection failures the rfcomm_sock_sendmsg() should return
an error and not a 0 value.

Signed-off-by: Victor Shcherbatyuk <victor.shcherbatyuk@tomtom.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>