cfg80211: fix can_beacon_sec_chan, reenable HT40

This follows wireless-testing 9236d838c920e90708570d9bbd7bb82d30a38130
("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 <[e-mail]>
Cc: [e-mail]
Acked-by: Luis R. Rodriguez <[e-mail]
Signed-off-by: John W. Linville <[e-mail]>

net/wireless/chan.c

···
 	switch (channel_type) {
 	case NL80211_CHAN_HT40PLUS:
 		diff = 20;
+		break;
 	case NL80211_CHAN_HT40MINUS:
 		diff = -20;
+		break;
 	default:
 		return false;
 	}