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>

include/linux/lightnvm.h

@@ -200,6 +200,7 @@ struct nvm_id {
 
 struct nvm_target {
 	struct list_head list;
+	struct nvm_dev *dev;
 	struct nvm_tgt_type *type;
 	struct gendisk *disk;
 };