block_cipher: add MBEDTLS_PRIVATE to new PSA fields in mbedtls_block_cipher_context_t

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/include/mbedtls/block_cipher.h b/include/mbedtls/block_cipher.h
index 535412a..2286a57 100644
--- a/include/mbedtls/block_cipher.h
+++ b/include/mbedtls/block_cipher.h
@@ -52,9 +52,9 @@
 typedef struct {
     mbedtls_block_cipher_id_t MBEDTLS_PRIVATE(id);
 #if defined(MBEDTLS_BLOCK_CIPHER_SOME_PSA)
-    mbedtls_block_cipher_engine_t engine;
-    psa_key_type_t psa_key_type;
-    mbedtls_svc_key_id_t psa_key_id;
+    mbedtls_block_cipher_engine_t MBEDTLS_PRIVATE(engine);
+    psa_key_type_t MBEDTLS_PRIVATE(psa_key_type);
+    mbedtls_svc_key_id_t MBEDTLS_PRIVATE(psa_key_id);
 #endif
     union {
         unsigned dummy; /* Make the union non-empty even with no supported algorithms. */