Staging: wlan-ng: removed "next" member of wlandevice_t since it is not used anywhere in code.

This patch removes "next" member of wlandevice_t since it
is not used anywhere in the wlan-ng code.

Signed-off-by: Claudiu Beznea <claudiu.beznea@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>