nvme: fix controller instance leak

If the driver has to unbind from the controller for an early failure
before the subsystem has been set up, there won't be a subsystem holding
the controller's instance, so the controller needs to free its own
instance in this case.

Fixes: 733e4b69 ("nvme: Assign subsys instance from first ctrl")
Signed-off-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>

drivers/nvme/host/core.c

@@ -4394,7 +4394,7 @@ static void nvme_free_ctrl(struct device *dev)
 	struct nvme_subsystem *subsys = ctrl->subsys;
 	struct nvme_cel *cel, *next;
 
-	if (subsys && ctrl->instance != subsys->instance)
+	if (!subsys || ctrl->instance != subsys->instance)
 		ida_simple_remove(&nvme_instance_ida, ctrl->instance);
 
 	list_for_each_entry_safe(cel, next, &ctrl->cels, entry) {