SSL: use MD_CAN macros

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/programs/ssl/ssl_test_lib.h b/programs/ssl/ssl_test_lib.h
index 64f557d..8540d1e 100644
--- a/programs/ssl/ssl_test_lib.h
+++ b/programs/ssl/ssl_test_lib.h
@@ -32,7 +32,7 @@
 #elif defined(MBEDTLS_ENTROPY_C) && defined(MBEDTLS_CTR_DRBG_C)
 #define HAVE_RNG
 #elif defined(MBEDTLS_ENTROPY_C) && defined(MBEDTLS_HMAC_DRBG_C) &&     \
-    (defined(MBEDTLS_SHA256_C) || defined(MBEDTLS_SHA512_C))
+    (defined(MBEDTLS_MD_CAN_SHA256) || defined(MBEDTLS_MD_CAN_SHA512))
 #define HAVE_RNG
 #endif