mac80211: Fix condition validating WMM IE

Commit c470bdc1 ("mac80211: don't WARN on bad WMM parameters from
buggy APs") handled cases where an AP reports a zeroed WMM
IE. However, the condition that checks the validity accessed the wrong
index in the ieee80211_tx_queue_params array, thus wrongly deducing
that the parameters are invalid. Fix it.

Fixes: c470bdc1 ("mac80211: don't WARN on bad WMM parameters from buggy APs")
Signed-off-by: Ilan Peer <ilan.peer@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>