staging: et131x: cancel_work when module gets unloaded

The work item has been added to the queue using INIT_WORK and scheduled
in interrupt handler. when module unloads that work item has not been
removed from the queue. remove and stop its further execution when the
module unloaded

Cc: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Devendra Naga <devendra.aaru@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>