After the previous similar bugfix there was another bug here,
if no VHT elements were found we also disabled HE. Fix this to
disable HE only on the 5 GHz band; on 6 GHz it was already not
disabled, and on 2.4 GHz there need (should) not be any VHT.

Fixes: 57fa5e85 ("mac80211: determine chandef from HE 6 GHz operation")
Link: https://lore.kernel.org/r/20201013140156.535a2fc6192f.Id6e5e525a60ac18d245d86f4015f1b271fce6ee6@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>