nvme: lightnvm: fix memory leak

Free up kmalloc allocated memory if failure happens while handling L2P
table transfer in nvme_nvm_get_l2p_tbl.

Fixes: 8e79b5cb

 ("lightnvm: move block provisioning to targets")
Signed-off-by: Rakesh Pandit <rakesh@tuxera.com>
Reviewed-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Jens Axboe <axboe@fb.com>