wifi: mt76: mt7996: Remove unnecessary link_id checks in mt7996_tx

wifi: mt76: mt7996: Remove unnecessary link_id checks in mt7996_tx

Remove unnecessary link_id checks in mt7996_tx routine since if the link
identifier provided by mac80211 is unspecified the value will be
overwritten at the beginning on the function.

Fixes: f940c9b7aef6 ("wifi: mt76: mt7996: Set proper link destination address in mt7996_tx()")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20250924-mt76_tx_unnecessary-check-v1-1-e595930a5662@kernel.org
Signed-off-by: Felix Fietkau <nbd@nbd.name>