staging: vt6656: covert RXvMngWorkItem to work queue

Tasklet to workqueue.
RxMngWorkItem -> rx_mng_work_item

Reduce atomic area of driver and dependency on system timer.

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>