media: dvbdev: drop refcount on error path in dvb_device_open()

If call to file->f_op->open() fails, then call dvb_device_put(dvbdev).

Fixes: 0fc044b2 ("media: dvbdev: adopts refcnt to avoid UAF")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

drivers/media/dvb-core/dvbdev.c

@@ -104,6 +104,8 @@ static int dvb_device_open(struct inode *inode, struct file *file)
 			err = file->f_op->open(inode, file);
 		up_read(&minor_rwsem);
 		mutex_unlock(&dvbdev_mutex);
+		if (err)
+			dvb_device_put(dvbdev);
 		return err;
 	}
 fail: