Fix minor issue in HT40 max rate determination

Commit a1b790eb9d7514d1a6e0582a07f695a1564caa59 ('Select AP based on
estimated maximum throughput') had a copy-paste bug than ended up
leaving one of the max_ht40_rate() cases unreachable. (CID 106087)

Signed-off-by: Jouni Malinen <j@w1.fi>
1 file changed