staging: vt6656: Remove variable fKillEventPollingThread

We already kill the urb and since patch
s_nsInterruptUsbIoCompleteRead add urb status returns.
have error handling

There is no need for this variable.

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