media: hdpvr: initialize dev->worker at hdpvr_register_videodev

hdpvr_register_videodev is responsible to initialize a worker in
hdpvr_device. However, the worker is only initialized at
hdpvr_start_streaming other than hdpvr_register_videodev.
When hdpvr_probe does not initialize its worker, the hdpvr_disconnect
will encounter one WARN in flush_work.The stack trace is as follows:

 hdpvr_disconnect+0xb8/0xf2 drivers/media/usb/hdpvr/hdpvr-core.c:425
 usb_unbind_interface+0xbf/0x3a0 drivers/usb/core/driver.c:458
 __device_release_driver drivers/base/dd.c:1206 [inline]
 device_release_driver_internal+0x22a/0x230 drivers/base/dd.c:1237
 bus_remove_device+0x108/0x160 drivers/base/bus.c:529
 device_del+0x1fe/0x510 drivers/base/core.c:3592
 usb_disable_device+0xd1/0x1d0 drivers/usb/core/message.c:1419
 usb_disconnect+0x109/0x330 drivers/usb/core/hub.c:2228

Fix this by moving the initialization of dev->worker to the starting of
hdpvr_register_videodev
Reported-by: Nsyzkaller <syzkaller@googlegroups.com>
Signed-off-by: NDongliang Mu <mudongliangabcd@gmail.com>
Signed-off-by: NHans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: NMauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/usb/hdpvr/hdpvr-video.c

@@ -308,7 +308,6 @@ static int hdpvr_start_streaming(struct hdpvr_device *dev)
 
 	dev->status = STATUS_STREAMING;
 
-	INIT_WORK(&dev->worker, hdpvr_transmit_buffers);
 	schedule_work(&dev->worker);
 
 	v4l2_dbg(MSG_BUFFER, hdpvr_debug, &dev->v4l2_dev,
@@ -1165,6 +1164,9 @@ int hdpvr_register_videodev(struct hdpvr_device *dev, struct device *parent,
 	bool ac3 = dev->flags & HDPVR_FLAG_AC3_CAP;
 	int res;
 
+	// initialize dev->worker
+	INIT_WORK(&dev->worker, hdpvr_transmit_buffers);
+
 	dev->cur_std = V4L2_STD_525_60;
 	dev->width = 720;
 	dev->height = 480;