mac80211: fix managed mode channel context use

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>
diff --git a/net/mac80211/mlme.c b/net/mac80211/mlme.c
index a355292..3b9cb51 100644
--- a/net/mac80211/mlme.c
+++ b/net/mac80211/mlme.c
@@ -3529,8 +3529,11 @@
 	 */
 	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;
 }