Replace PSA error code definitions with the ones defined in PSA spec
diff --git a/library/psa_crypto_storage.h b/library/psa_crypto_storage.h
index 85881c1..9da009d 100644
--- a/library/psa_crypto_storage.h
+++ b/library/psa_crypto_storage.h
@@ -84,7 +84,7 @@
  * \retval PSA_ERROR_INSUFFICIENT_MEMORY
  * \retval PSA_ERROR_INSUFFICIENT_STORAGE
  * \retval PSA_ERROR_STORAGE_FAILURE
- * \retval PSA_ERROR_OCCUPIED_SLOT
+ * \retval PSA_ERROR_ALREADY_EXISTS
  */
 psa_status_t psa_save_persistent_key( const psa_key_id_t key,
                                       const psa_key_type_t type,
@@ -115,7 +115,7 @@
  * \retval PSA_SUCCESS
  * \retval PSA_ERROR_INSUFFICIENT_MEMORY
  * \retval PSA_ERROR_STORAGE_FAILURE
- * \retval PSA_ERROR_EMPTY_SLOT
+ * \retval PSA_ERROR_DOES_NOT_EXIST
  */
 psa_status_t psa_load_persistent_key( psa_key_id_t key,
                                       psa_key_type_t *type,