mac80211: removed useless code in IBSS management

ieee82011_sta_find_ibss() and ieee80211_sta_merge_ibss() are always
called with a defined state. So it's useless to check it or set it in
those function.

Signed-off-by: Benoit Papillault <benoit.papillault@free.fr>
Signed-off-by: John W. Linville <linville@tuxdriver.com>