use mbedtls_ssl_session_init() to init session variable

Use mbedtls_ssl_session_init() to init variable just like
session-family APIs described

Signed-off-by: Benson Liou <benson.liou@sony.com>
diff --git a/programs/ssl/ssl_client2.c b/programs/ssl/ssl_client2.c
index 1b3dedb..05bb2ff 100644
--- a/programs/ssl/ssl_client2.c
+++ b/programs/ssl/ssl_client2.c
@@ -833,7 +833,7 @@
     mbedtls_net_init(&server_fd);
     mbedtls_ssl_init(&ssl);
     mbedtls_ssl_config_init(&conf);
-    memset(&saved_session, 0, sizeof(mbedtls_ssl_session));
+    mbedtls_ssl_session_init(&saved_session);
     rng_init(&rng);
 #if defined(MBEDTLS_SSL_HANDSHAKE_WITH_CERT_ENABLED)
     mbedtls_x509_crt_init(&cacert);