[PATCH] Driver core: Documentation: use S_IRUSR | ... in stead of 0644

Change filemode to use defines in stead of 0644,
based on suggestions by Walter Harms and Domen Puncer.

Signed-off-by: Jan Veldeman <Jan.Veldeman@advalvas.be>
Signed-off-by: Domen Puncer <domen@coderock.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>