haskell: fix package sets based on integer-simple

Fixes mass build failures in these package sets,
due to "unknown pacakge: integer-simple".

Attributes that demonstrate this (see before/after):

* haskell.packages.integer-simple.ghc843.hello
* haskell.packages.integer-simple.ghc802.scientific

The second one is from the NixOS manual, FWIW.

pkgs/top-level/haskell-packages.nix

@@ -200,6 +200,7 @@ in rec {
         (pkgs.lib.attrNames packages);
     in pkgs.lib.genAttrs integerSimpleGhcNames (name: packages."${name}".override {
       ghc = bh.compiler.integer-simple."${name}";
+      buildHaskellPackages = bh.packages.integer-simple."${name}";
       overrides = _self : _super : {
         integer-simple = null;
         integer-gmp = null;