Clarify TLS PRF algorithm description
@@ -4160,7 +4160,8 @@ static psa_status_t psa_key_derivation_tls12_prf_generate_next_block(
*
* The `psa_tls12_prf_key_derivation` structure saves the block
* `HMAC_hash(secret, A(i) + seed)` from which the output
- * is currently extracted as `output_block`.
+ * is currently extracted as `output_block` and where i is
+ * `block_number`.
*/
/* Save the hash context before using it, to preserve the hash state with
