lightnvm: remove mgt targets on mgt removal

Targets associated with a device manager are not freed on device
removal. They have to be manually removed before shutdown. Make sure
any outstanding targets are freed upon shutdown.

Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/include/linux/lightnvm.h b/include/linux/lightnvm.h
index 0e8e019..cde31ff 100644
--- a/include/linux/lightnvm.h
+++ b/include/linux/lightnvm.h
@@ -200,6 +200,7 @@
 
 struct nvm_target {
 	struct list_head list;
+	struct nvm_dev *dev;
 	struct nvm_tgt_type *type;
 	struct gendisk *disk;
 };