hplip: add missing dependency

Graphical programs (e.g. hp-setup) error with:

error: No module named enum

This adds the enum module which fixes the error

(cherry picked from commit 8308e41)

pkgs/misc/drivers/hplip/default.nix

@@ -77,6 +77,7 @@ pythonPackages.buildPythonApplication {
     sip
   ] ++ stdenv.lib.optionals withQt5 [
     pyqt5
+    enum-compat
   ];
 
   makeWrapperArgs = [ "--prefix" "PATH" ":" "${nettools}/bin" ];