Bluetooth: mgmt: Use command complete on success for set system config

The command status reply is only for failure. When completing set system
config command, the reply has to be command complete.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Reviewed-by: Alain Michaud <alainm@chromium.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>