staging: wilc1000: move hif_workqueue static variables to 'wilc' structure

Avoid use of static variable hif_workqueue and move it inside 'wilc'
structure.

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>