Fix memory corruption in an SSL test function

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/tests/suites/test_suite_ssl.function b/tests/suites/test_suite_ssl.function
index 0d5cea1..f24d1a4 100644
--- a/tests/suites/test_suite_ssl.function
+++ b/tests/suites/test_suite_ssl.function
@@ -5439,7 +5439,7 @@
     size_t min_in_len, in_len, max_in_len, i;
     /* TLS additional data is 13 bytes (hence the "lucky 13" name) */
     unsigned char add_data[13];
-    unsigned char ref_out[MBEDTLS_MD_MAX_SIZE];
+    unsigned char ref_out[MBEDTLS_HASH_MAX_SIZE];
     unsigned char *data = NULL;
     unsigned char *out = NULL;
     unsigned char rec_num = 0;