wifi: mac80211: use correct iftype HE cap

We already check that the right iftype capa exists,
but then don't use it. Assign it to a variable so we
can actually use it, and then do that.

Fixes: bac2fd3d

 ("mac80211: remove use of ieee80211_get_he_sta_cap()")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230604120651.0e908e5c5fdd.Iac142549a6144ac949ebd116b921a59ae5282735@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>