staging: wilc1000: rename u8ssidlen in struct hidden_net_info

This patch renames u8ssidlen to ssid_len that is a member of
hidden_net_info. There is no need to use u8 prefix to show data type so
just rename it.

Signed-off-by: Chaehyun Lim <chaehyun.lim@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>