library/tests: replace md_psa.h with psa_util.h as include file for MD conversion

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/tests/src/test_helpers/ssl_helpers.c b/tests/src/test_helpers/ssl_helpers.c
index d02d305..6233580 100644
--- a/tests/src/test_helpers/ssl_helpers.c
+++ b/tests/src/test_helpers/ssl_helpers.c
@@ -9,7 +9,7 @@
  */
 
 #include <test/ssl_helpers.h>
-#include "md_psa.h"
+#include "mbedtls/psa_util.h"
 
 #if defined(MBEDTLS_SSL_TLS_C)
 #if defined(MBEDTLS_SSL_HANDSHAKE_WITH_CERT_ENABLED)