batman-adv: Remove unnecessary check for orig_ifinfo not NULL

orig_ifinfo is dereferenced multiple times in batadv_iv_ogm_update_seqnos
before the check for NULL is done. The function also exists at the
beginning when orig_ifinfo would have been NULL. This makes the check at
the end unnecessary and only confuses the reader/code analyzers.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>