Fix key_id and owner_id accessor macros

The accessor macros for key_id and owner_id in the mbedtls_svc_key_id_t
need to have the MBEDTLS_PRIVATE() specifier as these fields are private

Signed-off-by: Antonio de Angelis <antonio.deangelis@arm.com>
diff --git a/include/psa/crypto_values.h b/include/psa/crypto_values.h
index 2f9a15a..9760e9a 100644
--- a/include/psa/crypto_values.h
+++ b/include/psa/crypto_values.h
@@ -2269,8 +2269,8 @@
 #else /* MBEDTLS_PSA_CRYPTO_KEY_ID_ENCODES_OWNER */
 
 #define MBEDTLS_SVC_KEY_ID_INIT ( (mbedtls_svc_key_id_t){ 0, 0 } )
-#define MBEDTLS_SVC_KEY_ID_GET_KEY_ID( id ) ( ( id ).key_id )
-#define MBEDTLS_SVC_KEY_ID_GET_OWNER_ID( id ) ( ( id ).owner )
+#define MBEDTLS_SVC_KEY_ID_GET_KEY_ID( id ) ( ( id ).MBEDTLS_PRIVATE(key_id) )
+#define MBEDTLS_SVC_KEY_ID_GET_OWNER_ID( id ) ( ( id ).MBEDTLS_PRIVATE(owner) )
 
 /** Utility to initialize a key identifier at runtime.
  *