ssl_helpers.c: add mbedtls_test prefix for tweak_tls13_certificate*

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 d17d8ac..52e288d 100644
--- a/tests/src/test_helpers/ssl_helpers.c
+++ b/tests/src/test_helpers/ssl_helpers.c
@@ -2131,7 +2131,7 @@
 #endif /* MBEDTLS_SSL_HANDSHAKE_WITH_CERT_ENABLED */
 
 #if defined(MBEDTLS_TEST_HOOKS)
-int tweak_tls13_certificate_msg_vector_len(
+int mbedtls_test_tweak_tls13_certificate_msg_vector_len(
     unsigned char *buf, unsigned char **end, int tweak,
     int *expected_result, mbedtls_ssl_chk_buf_ptr_args *args)
 {