tlan: cancel work at remove path

the work has been scheduled from interrupt, and not been
cancelled when the driver is unloaded, which doesn't remove
the work item from the global workqueue. call the
cancel_work_sync when the driver is removed (rmmod'ed).

Cc: Sriram <srk@ti.com>
Cc: Cyril Chemparathy <cyril@ti.com>
Cc: Vinay Hegde <vinay.hegde@ti.com>
Signed-off-by: Devendra Naga <devendra.aaru@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>