wifi: ath12k: fix Smatch warnings on ath12k_core_suspend()

Smatch is throwing below warning:

Commit 692921ea ("wifi: ath12k: flush all packets before
suspend") leads to the following Smatch static checker warning:

	drivers/net/wireless/ath/ath12k/core.c:58 ath12k_core_suspend()
	warn: sleeping in atomic context

and also gives the reason:

drivers/net/wireless/ath/ath12k/core.c
    48         int ret, i;
    49
    50         if (!ab->hw_params->supports_suspend)
    51                 return -EOPNOTSUPP;
    52
    53         rcu_read_lock();
               ^^^^^^^^^^^^^^^
Disables preemption.

    54         for (i = 0; i < ab->num_radios; i++) {
    55                 ar = ath12k_mac_get_ar_by_pdev_id(ab, i);
    56                 if (!ar)
    57                         continue;
--> 58                 ret = ath12k_mac_wait_tx_complete(ar);
                                        ^^^^^^^
Sleeping in atomic context.

    59                 if (ret) {
    60                         ath12k_warn(ab, "failed to wait tx complete: %d\n", ret);
    61                         rcu_read_unlock();
    62                         return ret;
    63                 }
    64         }
    65         rcu_read_unlock();

But it is weird that no warning on this in run time even with
CONFIG_DEBUG_ATOMIC_SLEEP=y. With some debug it is found that this is
because: when system goes to suspend, ath12k_mac_op_stop() gets called
where then in ath12k_mac_stop() ab->pdevs_active[ar->pdev_idx] is cleared.
This results in ath12k_mac_get_ar_by_pdev_id() always returning a NULL ar,
and thereby ath12k_mac_wait_tx_complete() never gets a chance to run.

Fix it by retrieving ar directly from ab->pdevs[].ar instead of using
ath12k_mac_get_ar_by_pdev_id(). Since ab->pdevs[].ar is set at boot time
and won't get cleared when suspend, ath12k_mac_wait_tx_complete() won't
be skipped. In addition, with ath12k_mac_get_ar_by_pdev_id() removed,
rcu_read_lock()/unlock() are not needed any more, so remove them. This
also fixes the warning above.

Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0-03427-QCAHMTSWPL_V1.0_V2.0_SILICONZ-1.15378.4

Fixes: 692921ea ("wifi: ath12k: flush all packets before suspend")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/ath12k/7a96ca11-80b5-4751-8cfc-fa637f3aa63a@moroto.mountain/Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
Acked-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20240511095045.9623-1-quic_bqiang@quicinc.com

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

@@ -50,19 +50,16 @@ int ath12k_core_suspend(struct ath12k_base *ab)
 	if (!ab->hw_params->supports_suspend)
 		return -EOPNOTSUPP;
 
-	rcu_read_lock();
 	for (i = 0; i < ab->num_radios; i++) {
-		ar = ath12k_mac_get_ar_by_pdev_id(ab, i);
+		ar = ab->pdevs[i].ar;
 		if (!ar)
 			continue;
 		ret = ath12k_mac_wait_tx_complete(ar);
 		if (ret) {
 			ath12k_warn(ab, "failed to wait tx complete: %d\n", ret);
-			rcu_read_unlock();
 			return ret;
 		}
 	}
-	rcu_read_unlock();
 
 	/* PM framework skips suspend_late/resume_early callbacks
 	 * if other devices report errors in their suspend callbacks.