nl80211: fix NL80211_ATTR_HE_6GHZ_CAPABILITY usage

nl80211: fix NL80211_ATTR_HE_6GHZ_CAPABILITY usage

In nl80211_set_station(), we check NL80211_ATTR_HE_6GHZ_CAPABILITY
and then use NL80211_ATTR_HE_CAPABILITY, which is clearly wrong.
Fix this to use NL80211_ATTR_HE_6GHZ_CAPABILITY as well.

Cc: stable@vger.kernel.org
Fixes: 9236ff59b5b6 ("cfg80211: handle 6 GHz capability of new station")
Link: https://lore.kernel.org/r/20200805153516.310cef625955.I0abc04dc8abb2c7c005c88ef8fa2d0e3c9fb95c4@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>