haskell.compiler.ghc948: fix expression file name

This is a left over to do from #308776. Rebasing existing PR (prior
to #308776) would need to be rebased on a change before the commit
included in this PR.

pkgs/top-level/haskell-packages.nix

@@ -229,7 +229,7 @@ in {
       buildTargetLlvmPackages = pkgsBuildTarget.llvmPackages_12;
       llvmPackages = pkgs.llvmPackages_12;
     };
-    ghc948 = callPackage ../development/compilers/ghc/9.4.8.fixme.nix {
+    ghc948 = callPackage ../development/compilers/ghc/9.4.8.nix {
       bootPkgs =
         # Building with 9.2 is broken due to
         # https://gitlab.haskell.org/ghc/ghc/-/issues/21914