lightnvm: pblk: ignore the smeta oob area scan

The smeta area l2p mapping is empty, and actually the
recovery procedure only need to restore data sector's l2p
mapping. So ignore the smeta oob scan.

Signed-off-by: Zhoujie Wu <zjwu@marvell.com>
Reviewed-by: Javier González <javier@javigon.com>
Reviewed-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>