Bluetooth: Fix using uninitialized variable when pairing

Commit 6c53823a reshuffled the way the
authentication requirement gets set in the hci_io_capa_request_evt()
function, but at the same time it failed to update an if-statement where
cp.authentication is used before it has been initialized. The correct
value the code should be looking for in this if-statement is
conn->auth_type.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Cc: stable@vger.kernel.org # 3.16