ssl_helpers.c: change prefix and move *certificate_free to static

Signed-off-by: Yanray Wang <yanray.wang@arm.com>
diff --git a/tests/src/test_helpers/ssl_helpers.c b/tests/src/test_helpers/ssl_helpers.c
index abbe957..a55df1b 100644
--- a/tests/src/test_helpers/ssl_helpers.c
+++ b/tests/src/test_helpers/ssl_helpers.c
@@ -577,7 +577,7 @@
 /*
  * Deinitializes certificates from endpoint represented by \p ep.
  */
-void mbedtls_endpoint_certificate_free(mbedtls_test_ssl_endpoint *ep)
+static void test_ssl_endpoint_certificate_free(mbedtls_test_ssl_endpoint *ep)
 {
     mbedtls_test_ssl_endpoint_certificate *cert = &(ep->cert);
     if (cert != NULL) {
@@ -729,7 +729,7 @@
 
 exit:
     if (ret != 0) {
-        mbedtls_endpoint_certificate_free(ep);
+        test_ssl_endpoint_certificate_free(ep);
     }
 
     return ret;
@@ -845,7 +845,7 @@
     mbedtls_test_ssl_endpoint *ep,
     mbedtls_test_message_socket_context *context)
 {
-    mbedtls_endpoint_certificate_free(ep);
+    test_ssl_endpoint_certificate_free(ep);
 
     mbedtls_ssl_free(&(ep->ssl));
     mbedtls_ssl_config_free(&(ep->conf));