lightnvm: use kobj_to_dev()

This fixs coccicheck warning:

drivers/nvme//host/lightnvm.c:1243:60-61: WARNING opportunity for
kobj_to_dev()

Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Matias Bjørling <matias.bjorling@wdc.com>
Link: https://lore.kernel.org/r/20210413105257.159260-2-matias.bjorling@wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/nvme/host/lightnvm.c

@@ -1240,7 +1240,7 @@ static struct attribute *nvm_dev_attrs[] = {
 static umode_t nvm_dev_attrs_visible(struct kobject *kobj,
 				     struct attribute *attr, int index)
 {
-	struct device *dev = container_of(kobj, struct device, kobj);
+	struct device *dev = kobj_to_dev(kobj);
 	struct gendisk *disk = dev_to_disk(dev);
 	struct nvme_ns *ns = disk->private_data;
 	struct nvm_dev *ndev = ns->ndev;