My commit 
f2d9d270c15ae0139b54a7e7466d738327e97e03
("mac80211: support VHT association") introduced a
very stupid bug: the loop to downgrade the channel
width never attempted to actually use it again so
it would downgrade all the way to 20_NOHT. Fix it.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
         */
        ret = ieee80211_vif_use_channel(sdata, &chandef,
                                        IEEE80211_CHANCTX_SHARED);
-       while (ret && chandef.width != NL80211_CHAN_WIDTH_20_NOHT)
+       while (ret && chandef.width != NL80211_CHAN_WIDTH_20_NOHT) {
                ifmgd->flags |= chandef_downgrade(&chandef);
+               ret = ieee80211_vif_use_channel(sdata, &chandef,
+                                               IEEE80211_CHANCTX_SHARED);
+       }
        return ret;
 }