cfg80211: fix can_beacon_sec_chan, reenable HT40

This follows wireless-testing 9236d838
("cfg80211: fix extension channel checks to initiate communication") and
fixes accidental case fall-through. Without this fix, HT40 is entirely
blocked.
Signed-off-by: Mark Mentovai <mark@moxienet.com>
Cc: stable@kernel.org
Acked-by: Luis R. Rodriguez <lrodriguez@atheros.com
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/wireless/chan.c

@@ -54,8 +54,10 @@ static bool can_beacon_sec_chan(struct wiphy *wiphy,
 	switch (channel_type) {
 	case NL80211_CHAN_HT40PLUS:
 		diff = 20;
+		break;
 	case NL80211_CHAN_HT40MINUS:
 		diff = -20;
+		break;
 	default:
 		return false;
 	}