nixos/sudo-rs: add crossCompile 'fix'

This is just a quick fix based on pname,
as I have no idea how to use slicing in the module

We should instead use slicing to get the package for the host

nixos/modules/security/sudo-rs.nix

···
             src = pkgs.writeText "sudoers-in" cfg.configFile;
             preferLocalBuild = true;
           }
-          "${cfg.package}/bin/visudo -f $src -c && cp $src $out";
+          "${pkgs.buildPackages."${cfg.package.pname}"}/bin/visudo -f $src -c && cp $src $out";
         mode = "0440";
       };