wifi: mac80211: pass 'sta' to ieee80211_rx_data_set_sta()

There's at least one case in ieee80211_rx_for_interface()
where we might pass &((struct sta_info *)NULL)->sta to it
only to then do container_of(), and then checking the
result for NULL, but checking the result of container_of()
for NULL looks really odd.

Fix this by just passing the struct sta_info * instead.

Fixes: e66b7920 ("wifi: mac80211: fix initialization of rx->link and rx->link_sta")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>