Add buffer size macro for psa_get_key_domain_parameters
diff --git a/include/psa/crypto.h b/include/psa/crypto.h
index 6356c58..e8f9a18 100644
--- a/include/psa/crypto.h
+++ b/include/psa/crypto.h
@@ -447,6 +447,10 @@
* \param[in] attributes The key attribute structure to query.
* \param[out] data On success, the key domain parameters.
* \param data_size Size of the \p data buffer in bytes.
+ * The buffer is guaranteed to be large
+ * enough if its size in bytes is at least
+ * the value given by
+ * PSA_KEY_DOMAIN_PARAMETERS_SIZE().
* \param[out] data_length On success, the number of bytes
* that make up the key domain parameters data.
*