nvme: put ns_head ref if namespace fails allocation

In case nvme_alloc_ns fails after we initialize ns_head but before we
add the ns to the controller namespaces list we need to explicitly put
the ns_head reference because when we teardown the controller we
won't find it, causing us to leak a dangling subsystem eventually.
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/nvme/host/core.c

@@ -3304,6 +3304,7 @@ static int nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid)
 	mutex_lock(&ctrl->subsys->lock);
 	list_del_rcu(&ns->siblings);
 	mutex_unlock(&ctrl->subsys->lock);
+	nvme_put_ns_head(ns->head);
  out_free_id:
 	kfree(id);
  out_free_queue: