address @reynir review comments

rng/hmac_drbg.ml

@@ -27,7 +27,7 @@ module Make (H : Digestif.S) = struct
   let generate_into ~g buf ~off len =
     if not g.seeded then raise Rng.Unseeded_generator ;
     let rec go off k v = function
-      | 0 -> v (* unlikely this happens *)
+      | 0 -> v
       | 1 ->
         let v = H.hmac_string ~key:k v |> H.to_raw_string in
         let len =

rng/mirage_crypto_rng.mli

@@ -230,14 +230,14 @@ val unset_default_generator : unit -> unit
 (** [unset_default_generator ()] sets the default generator to [None]. *)
 (**/**)
 
-val generate : ?g:g -> int -> string
-(** Invoke {{!Generator.generate}generate} on [g] or
-    {{!generator}default generator}. *)
-
 val generate_into : ?g:g -> bytes -> ?off:int -> int -> unit
 (** Invoke {{!Generator.generate}generate} on [g] or
     {{!generator}default generator}. The offset [off] defaults to 0. *)
 
+val generate : ?g:g -> int -> string
+(** Invoke {generate_into} on [g] or {{!generator}default generator} and a
+    freshly allocated bytes buffer that is converted to a string. *)
+
 val block : g option -> int
 (** {{!Generator.block}Block} size of [g] or
     {{!generator}default generator}. *)