Bluetooth: Fix memory leak in hci_connect_le_scan

In the implementation of hci_connect_le_scan() when conn is added via
hci_conn_add(), if hci_explicit_conn_params_set() fails the allocated
memory for conn is leaked. Use hci_conn_del() to release it.

Fixes: f75113a2 ("Bluetooth: add hci_connect_le_scan")
Signed-off-by: Navid Emamdoost <navid.emamdoost@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>