mac80211: free skb in WEP error case

If, for some strange reason, ieee80211_wep_encrypt() fails in
ieee80211_send_auth() free the SKB instead of sending out the
useless frame, in addition to the warning. This can't really
happen since the SKB was freshly allocated.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20210618133832.98f058d7a8b2.Ie605e6a10e72eae02f5734032826af48b85b6d11@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>