staging: wilc1000: remove duplicate netdev

There are two net_device pointer which is the same because two structures
are merged into wilc_vif in previous patch. Remove wilc_netdev and change
with ndev.

Signed-off-by: Glen Lee <glen.lee@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>