lightnvm: do not reserve lun on l2p loading

When the l2p table is loaded, addresses are checked for the lun they
belong to and luns are reserved accordingly. This assumes that metadata
is being stored in the backend device to recover the previous target
configuration. Since this is not yet implemented, this check collides
with some of the core initialization (e.g., sysblock initialization when
a page is formed by several sectors).

We take this check out and for now rely on that the right target will be
created instead. When metadata is stored to recover a target, this check
will come natural as part of the recovery strategy.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>