wifi: ath11k: simplify ath11k_mac_validate_vht_he_fixed_rate_settings()

In ath11k_mac_validate_vht_he_fixed_rate_settings() ar->ab->peers
list is not altered so list_for_each_entry() should be safe.

Compile tested only.

Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20230726092113.78794-1-dmantipov@yandex.ru