Cleanup debug_fn
Cleanup debug_fn to better match coding conventions.
Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>
Reviewed-by: Stephen Gallagher <sgallagh@redhat.com>
Reviewed-by: Simo Sorce <simo@redhat.com>
(cherry picked from commit 1eedbd1bd2037437f5b9aed1f4061af396ef6733)