emacs: Fix reference to directory variable.

This is a followup to commit 7741139080.

* emacs/guix-emacs.el (guix-emacs-find-autoloads): Fix variable
  reference to 'elisp-root-dir'.

Signed-off-by: Alex Kost <alezost@gmail.com>

emacs/guix-emacs.el

@@ -69,7 +69,7 @@ Return nil if there are no emacs packages installed in PROFILE."
                                 (guix-emacs-subdirs elisp-pkgs-dir))))
                 (append root-autoloads pkgs-autoloads))
             root-autoloads))
-      (message "Directory '%s' does not exist." dir)
+      (message "Directory '%s' does not exist." elisp-root-dir)
       nil)))
 
 ;;;###autoload