lightnvm: pblk: reduce arguments in __pblk_rb_update_l2p

We already pass the structure pointer so no need to pass the member.

Signed-off-by: Rakesh Pandit <rakesh@tuxera.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>