mfcl8690cdwlpr: Make it installable on x86_64-linux

This seems like a strange omission, because it works without a hitch.
Tested using cups and mfcl8690cdwcupswrapper, which uses this package.

pkgs/misc/cups/drivers/mfcl8690cdwlpr/default.nix

@@ -41,6 +41,6 @@ stdenv.mkDerivation rec {
     sourceProvenance = with lib.sourceTypes; [ binaryNativeCode ];
     license = lib.licenses.unfree;
     maintainers = [ ];
-    platforms = [ "i686-linux" ];
+    platforms = [ "x86_64-linux" "i686-linux" ];
   };
 }