Nix Flake: Fix overlay (again) (#3196)

flake.nix

@@ -46,8 +46,11 @@
                 };
           });
 
-      overlays.default = final: prev: {
+      overlays = {
+        default = self.overlays.waybar;
+        waybar = final: prev: {
           waybar = final.callPackage ./nix/default.nix {
+            waybar = prev.waybar;
             # take the first "version: '...'" from meson.build
             version =
               (builtins.head (builtins.split "'"
@@ -57,11 +60,11 @@
               + "+date=" + (mkDate (self.lastModifiedDate or "19700101")) + "_" + (self.shortRev or "dirty");
           };
         };
+      };
 
-      packages = genSystems (pkgs:
-        let packages = self.overlays.default pkgs pkgs;
-        in packages // {
-          default = packages.waybar;
+      packages = genSystems (pkgs: {
+        default = self.packages.${pkgs.stdenv.hostPlatform.system}.waybar;
+        inherit (pkgs) waybar;
       });
     };
 }