Bluetooth: use memset avoid memory leaks

Use memset to initialize structs to prevent memory leaks
in l2cap_ecred_connect

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Minghao Chi (CGEL ZTE) <chi.minghao@zte.com.cn>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>