staging: wilc1000: fix kbuild test robot error

This patch fixes build warning and error reported by kbuild test robot.
It is fixed by including netdevice.h.

>> drivers/staging/wilc1000/wilc_wlan_if.h:940:27: warning: 'struct net_device'
 declared inside parameter list
    int wilc_wlan_init(struct net_device *dev, wilc_wlan_inp_t *inp);
>> drivers/staging/wilc1000/wilc_wlan_if.h:940:27: warning: its scope is only
 this definition or declaration, which is probably not what you want
>> drivers/staging/wilc1000/wilc_wlan.c:1954:5: error: conflicting types for
 'wilc_wlan_init'
    int wilc_wlan_init(struct net_device *dev, wilc_wlan_inp_t *inp)

Fixes: 30135ce ("staging: wilc1000: wilc_wlan_init: add argument struct net_device")
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Glen Lee <glen.lee@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wilc1000/wilc_wlan_if.h

@@ -12,6 +12,7 @@
 
 #include <linux/semaphore.h>
 #include "linux_wlan_common.h"
+#include <linux/netdevice.h>
 
 /********************************************
  *