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/library/pk.c b/library/pk.c
index 61ac0df..9261837 100644
--- a/library/pk.c
+++ b/library/pk.c
@@ -31,7 +31,7 @@
 
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
 #include "psa_util_internal.h"
-#include "md_psa.h"
+#include "mbedtls/psa_util.h"
 #endif
 
 #include <limits.h>