[[PATCH for-4.17 v1]] tools/ocaml/xenstored/store.ml: fix build error

[Edwin Török <edvin.torok@xxxxxxxxxx>]

Building with Dune in release mode fails with:
```
File "ocaml/xenstored/store.ml", line 464, characters 13-32:
Warning 18: this type-based record disambiguation is not principal.
File "ocaml/xenstored/store.ml", line 1:
Error: Some fatal warnings were triggered (1 occurrences)
```

This is a warning to help keep the code futureproof, quoting from its
documentation:
> Check information path during type-checking, to make sure that all types are
> derived in a principal way. When using labelled arguments and/or polymorphic
> methods, this flag is required to ensure future versions of the compiler will
> be able to infer types correctly, even if internal algorithms change. All
> programs accepted in -principal mode are also accepted in the default mode 
> with
> equivalent types, but different binary signatures, and this may slow down type
> checking; yet it is a good idea to use it once before publishing source code.

Fixes: db471408edd46 "tools/ocaml/xenstored: Fix quota bypass on domain 
shutdown"

Signed-off-by: Edwin Török <edvin.torok@xxxxxxxxxx>
---
 tools/ocaml/xenstored/store.ml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/ocaml/xenstored/store.ml b/tools/ocaml/xenstored/store.ml
index 14ec404988..38a4945372 100644
--- a/tools/ocaml/xenstored/store.ml
+++ b/tools/ocaml/xenstored/store.ml
@@ -461,7 +461,7 @@ let reset_permissions store domid =
       | Some perms ->
         if perms <> node.perms then
           Logging.debug "store|node" "Changed permissions for node %s" 
(Node.get_name node);
-        Some { node with perms }
+        Some { node with Node.perms }
     ) store.root
 
 type ops = {
-- 
2.34.1