wifi: ath12k: fix htt mlo-offset event locking

The ath12k active pdevs are protected by RCU but the htt mlo-offset
event handling code calling ath12k_mac_get_ar_by_pdev_id() was not
marked as a read-side critical section.

Mark the code in question as an RCU read-side critical section to avoid
any potential use-after-free issues.

Compile tested only.

Fixes: d8899132 ("wifi: ath12k: driver for Qualcomm Wi-Fi 7 devices")
Cc: stable@vger.kernel.org      # v6.2
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Acked-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20231019113650.9060-3-johan+linaro@kernel.org

drivers/net/wireless/ath/ath12k/dp_rx.c

@@ -1658,11 +1658,12 @@ static void ath12k_htt_mlo_offset_event_handler(struct ath12k_base *ab,
 	msg = (struct ath12k_htt_mlo_offset_msg *)skb->data;
 	pdev_id = u32_get_bits(__le32_to_cpu(msg->info),
 			       HTT_T2H_MLO_OFFSET_INFO_PDEV_ID);
-	ar = ath12k_mac_get_ar_by_pdev_id(ab, pdev_id);
 
+	rcu_read_lock();
+	ar = ath12k_mac_get_ar_by_pdev_id(ab, pdev_id);
 	if (!ar) {
 		ath12k_warn(ab, "invalid pdev id %d on htt mlo offset\n", pdev_id);
-		return;
+		goto exit;
 	}
 
 	spin_lock_bh(&ar->data_lock);
@@ -1678,6 +1679,8 @@ static void ath12k_htt_mlo_offset_event_handler(struct ath12k_base *ab,
 	pdev->timestamp.mlo_comp_timer = __le32_to_cpu(msg->mlo_comp_timer);
 
 	spin_unlock_bh(&ar->data_lock);
+exit:
+	rcu_read_unlock();
 }
 
 void ath12k_dp_htt_htc_t2h_msg_handler(struct ath12k_base *ab,