wifi: cfg80211: fix assoc response warning on failed links

The warning here shouldn't be done before we even set the
bss field (or should've used the input data). Move the
assignment before the warning to fix it.

We noticed this now because of Wen's bugfix, where the bug
fixed there had previously hidden this other bug.

Fixes: 53ad07e9 ("wifi: cfg80211: support reporting failed links")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>