mac80211: remove bogus skb vif assignment

The call to ieee80211_txq_enqueue overwrites the vif pointer with the
codel enqueue time, so setting it just before that call makes no sense.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>