mac80211: avoid using uninitialized stack data

commit 7e6225a1604d0c6aa4140289bf5761868ffc9c83 upstream.

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

Fixes: f3000e1b ("mac80211: fix broken use of VHT/20Mhz with some APs")
Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>