nvme: fix kernel paging oops

free the controller discard_page correctly.

Fixes: cb5b7262 ("nvme: provide fallback for discard alloc failure")
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/nvme/host/core.c

@@ -3596,7 +3596,7 @@ static void nvme_free_ctrl(struct device *dev)
 	ida_simple_remove(&nvme_instance_ida, ctrl->instance);
 	kfree(ctrl->effects);
 	nvme_mpath_uninit(ctrl);
-	kfree(ctrl->discard_page);
+	__free_page(ctrl->discard_page);
 
 	if (subsys) {
 		mutex_lock(&subsys->lock);