Add accessor helpers for mbedtls_test_info

Step one of being able to control access to mbedtls_test_info with
a mutex.

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/programs/ssl/ssl_test_lib.c b/programs/ssl/ssl_test_lib.c
index b49dd67..d4511ac 100644
--- a/programs/ssl/ssl_test_lib.c
+++ b/programs/ssl/ssl_test_lib.c
@@ -427,7 +427,7 @@
     mbedtls_test_mutex_usage_check();
 #endif
 
-    if (mbedtls_test_info.result != MBEDTLS_TEST_RESULT_SUCCESS) {
+    if (mbedtls_test_get_result() != MBEDTLS_TEST_RESULT_SUCCESS) {
         return 1;
     }
     return 0;