Further code optimizations

Signed-off-by: Przemek Stekiel <przemyslaw.stekiel@mobica.com>
diff --git a/programs/ssl/ssl_test_lib.c b/programs/ssl/ssl_test_lib.c
index ea422e9..26824c2 100644
--- a/programs/ssl/ssl_test_lib.c
+++ b/programs/ssl/ssl_test_lib.c
@@ -465,9 +465,9 @@
     return 0;
 }
 
-uint16_t *mbedtls_ssl_ffdh_supported_groups(void)
+const uint16_t *mbedtls_ssl_ffdh_supported_groups(void)
 {
-    static uint16_t ffdh_groups[] = {
+    static const uint16_t ffdh_groups[] = {
         MBEDTLS_SSL_IANA_TLS_GROUP_FFDHE2048,
         MBEDTLS_SSL_IANA_TLS_GROUP_FFDHE3072,
         MBEDTLS_SSL_IANA_TLS_GROUP_FFDHE4096,