staging: wilc1000: fixes variable dereferenced before check

This patch fixes the warning reported by smatch.
 - wilc_wlan_get_firmware() warn: variable dereferenced before check 'vif'
 - wilc_set_multicast_list() warn: variable dereferenced before check 'dev'

Just delete them and no need add null check since they are net_device from
ndo_set_rx_mode of net_device_ops and vif of netdev_priv.

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