staging: wilc1000: wilc1000_wlan_deinit: change argument and use wilc

This patch changes function argument wilc with net_device and use nic->wilc
instead of global variable g_linux_wlan. The null check codes should be placed
before it is used so move it.

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