qc71_laptop: rectify meta.platforms

This package is not expected to build in other platforms and
has been failing aarch64-linux in Hydra for years:
https://hydra.nixos.org/eval/1790516?filter=qc71&compare=1790473
https://hydra.nixos.org/eval/1795290?filter=qc71&compare=1795271
https://hydra.nixos.org/eval/1807986?filter=qc71&compare=1807946

pkgs/os-specific/linux/qc71_laptop/default.nix

···
     homepage = "https://github.com/pobrn/qc71_laptop/";
     license = licenses.gpl2Only;
     maintainers = with maintainers; [ aacebedo ];
-    platforms = platforms.linux;
+    platforms = [ "x86_64-linux" ];
   };
 }