The chunk metadata is allocated with vmalloc, so we need to use
vfree to free it.

Fixes: 090ee26f ("lightnvm: use internal allocation for chunk log page")
Signed-off-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Reviewed-by: Javier González <javier@javigon.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>