Avoid a case where we would access uninitialized stack data if the AP
advertises HT support without 40MHz channel support.

Cc: stable@vger.kernel.org
Fixes: f3000e1b ("mac80211: fix broken use of VHT/20Mhz with some APs")
Signed-off-by: NJes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>