[media] em28xx: Only deallocate struct em28xx after finishing all extensions

We can't free struct em28xx while one of the extensions is still
using it.

So, add a kref() to control it, freeing it only after the
extensions fini calls.

Reviewed-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/usb/em28xx/em28xx-dvb.c

@@ -1043,7 +1043,6 @@ static int em28xx_dvb_init(struct em28xx *dev)
 	em28xx_info("Binding DVB extension\n");
 
 	dvb = kzalloc(sizeof(struct em28xx_dvb), GFP_KERNEL);
-
 	if (dvb == NULL) {
 		em28xx_info("em28xx_dvb: memory allocation failed\n");
 		return -ENOMEM;
@@ -1521,6 +1520,9 @@ static int em28xx_dvb_init(struct em28xx *dev)
 	dvb->adapter.mfe_shared = mfe_shared;
 
 	em28xx_info("DVB extension successfully initialized\n");
+
+	kref_get(&dev->ref);
+
 ret:
 	em28xx_set_mode(dev, EM28XX_SUSPEND);
 	mutex_unlock(&dev->lock);
@@ -1577,6 +1579,7 @@ static int em28xx_dvb_fini(struct em28xx *dev)
 		em28xx_unregister_dvb(dvb);
 		kfree(dvb);
 		dev->dvb = NULL;
+		kref_put(&dev->ref, em28xx_free_device);
 	}
 
 	return 0;