tuningsysfs: fix msg typo

fix 'Managmenet' typo.

Reported-by: Gijs Hillenius <gijs@hillenius.net>
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
tuningsysfs: use lib process_directory() helper

use process_directory() helper while processing sata tunables.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>