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: NHans Holmberg <hans.holmberg@cnexlabs.com>
Reviewed-by: NJavier González <javier@javigon.com>
Signed-off-by: NMatias Bjørling <mb@lightnvm.io>
Signed-off-by: NJens Axboe <axboe@kernel.dk>