wifi: mt76: mt7996: Fix possible token leak in mt7996_tx_prepare_skb()

wifi: mt76: mt7996: Fix possible token leak in mt7996_tx_prepare_skb()

If link_conf or link_sta lookup fails in mt7996_tx_prepare_skb routine,
mt7996 driver leaks an already allocated tx token. Fix the issue
releasing the token in case of error.

Fixes: 7ef0c7ad735b0 ("wifi: mt76: mt7996: Implement MLD address translation for EAPOL")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20260531-mt7996_tx_prepare_skb-token-leack-v1-1-2b9c9f59ceb1@kernel.org
Signed-off-by: Felix Fietkau <nbd@nbd.name>