wifi: ath12k: relax list iteration in ath12k_mac_vif_unref()

In ath12k_mac_vif_unref() dp->tx_desc_used_list[i]
is not altered so list_for_each_entry() should be safe.

Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20230704173718.73462-1-dmantipov@yandex.ru