media: pvrusb2: fix memory leak in pvr_probe

In the Linux kernel, the following vulnerability has been resolved: media: pvrusb2: fix memory leak in pvr_probe The error handling code in pvr2_hdw_create forgets to unregister the v4l2 device. When pvr2_hdw_create returns back to pvr2_context_create, it calls pvr2_context_destroy to destroy context, but mp->hdw is NULL, which leads to that pvr2_hdw_destroy directly returns. Fix this by adding v4l2_device_unregister to decrease the refcount of usb interface.