org-fixup.el: Use defvar instead of defconst to define the `org-odt-data-dir' autoload

* org-fixup.el (org-make-org-version): Use defvar instead of
defconst to define the `org-odt-data-dir' autoload.

Thanks to Glenn Morris for pointing at this.

mk/org-fixup.el

@@ -52,7 +52,7 @@ the Git work tree)."
    (let ((org-git-version \"" org-git-version "\"))
      org-git-version))
 ;;;\#\#\#autoload
-\(defconst org-odt-data-dir \"" odt-dir "\"
+\(defvar org-odt-data-dir \"" odt-dir "\"
   \"The location of ODT styles.\")
 \f\n\(provide 'org-version\)
 \f\n;; Local Variables:\n;; version-control: never