lru_cache: Converted lc_seq_printf_status to return void

Fix the semantic of lc_seq_printf. Currently, it always returns 0 and
the return value is unused, therefore, convert the return type to void.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@fb.com>