wilc1000: use wilc handler as cookie in request_threaded_irq()

Use same cookie for request_threaded_irq() & free_irq() to properly free
IRQ during module unload. free_irq() already uses *wilc* handler so the
changes are required for request_threaded_irq().

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210225042302.17048-1-ajay.kathat@microchip.com