wifi: ath11k: fix dfs radar event locking

wifi: ath11k: fix dfs radar event locking

The ath11k active pdevs are protected by RCU but the DFS radar event
handling code calling ath11k_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: d5c65159f289 ("ath11k: driver for Qualcomm IEEE 802.11ax devices")
Cc: stable@vger.kernel.org      # 5.6
Acked-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20231019153115.26401-3-johan+linaro@kernel.org