batman-adv: Fix kernel panic when fetching vis data on a vis server

The hash_iterate removal introduced a bug leading to a kernel panic when
fetching the vis data on a vis server. That commit forgot to rename one
variable name, which this commit fixes now.

Reported-by: Russell Senior <russell@personaltelco.net>
Signed-off-by: Linus Lüssing <linus.luessing@web.de>
Signed-off-by: Sven Eckelmann <sven@narfation.org>