wifi: wilc1000: use existing iftype variable to store the interface type

For consistency, use an existing 'iftype' element which was already
having the interface type. Replace 'mode' with 'iftype' as it was used
for the same purpose.

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220720160302.231516-8-ajay.kathat@microchip.com