[PATCH 10/12] [media] dvb_frontend: move kref to struct dvb_frontend

This commit amends my old commit fe35637b0a9f ("[media] dvb_frontend: eliminate blocking wait in dvb_unregister_frontend()"), which added kref to struct dvb_frontend_private. It turned out that there are several use-after-free bugs left, which affect the struct dvb_frontend. Protecting it with

[PATCH 10/12] [media] dvb_frontend: move kref to struct dvb_frontend

This commit amends my old commit fe35637b0a9f ("[media] dvb_frontend: eliminate blocking wait in dvb_unregister_frontend()"), which added kref to struct dvb_frontend_private. It turned out that there are several use-after-free bugs left, which affect the struct dvb_frontend. Protecting it with