wifi: mt76: mt7996: fix teardown command for an MLD peer

wifi: mt76: mt7996: fix teardown command for an MLD peer

For an MLD peer, we only need to call the teardown command when removing
the last link, and there's no need to call mt7996_mcu_add_sta() for the
earlier links.

Fixes: c1d6dd5d03eb ("wifi: mt76: mt7996: Add mt7996_mcu_teardown_mld_sta rouine")
Signed-off-by: Shayne Chen <shayne.chen@mediatek.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20251106064203.1000505-6-shayne.chen@mediatek.com
Signed-off-by: Felix Fietkau <nbd@nbd.name>