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: syzkaller <syzkaller@googlegroups.com>
Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>