pnpm.fetchDeps: fix use for cross

pkgs/development/tools/pnpm/generic.nix

···
   withNode ? true,
   version,
   hash,
+  buildPackages,
 }:
 let
   majorVersion = lib.versions.major version;
···
 
   passthru =
     let
-      fetchDepsAttrs = callPackages ./fetch-deps { pnpm = finalAttrs.finalPackage; };
+      fetchDepsAttrs = callPackages ./fetch-deps {
+        pnpm = buildPackages."pnpm_${lib.versions.major version}";
+      };
     in
     {
       inherit (fetchDepsAttrs) fetchDeps configHook;