Provide and use internal function mbedtls_zeroize_and_free()

Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
diff --git a/library/ssl_tls12_client.c b/library/ssl_tls12_client.c
index 4d8442e..5a98165 100644
--- a/library/ssl_tls12_client.c
+++ b/library/ssl_tls12_client.c
@@ -3459,16 +3459,14 @@
     }
 
     if (ssl->session != NULL && ssl->session->ticket != NULL) {
-        mbedtls_platform_zeroize(ssl->session->ticket,
+        mbedtls_zeroize_and_free(ssl->session->ticket,
                                  ssl->session->ticket_len);
-        mbedtls_free(ssl->session->ticket);
         ssl->session->ticket = NULL;
         ssl->session->ticket_len = 0;
     }
 
-    mbedtls_platform_zeroize(ssl->session_negotiate->ticket,
+    mbedtls_zeroize_and_free(ssl->session_negotiate->ticket,
                              ssl->session_negotiate->ticket_len);
-    mbedtls_free(ssl->session_negotiate->ticket);
     ssl->session_negotiate->ticket = NULL;
     ssl->session_negotiate->ticket_len = 0;