wifi: ath11k: fix htt pktlog locking

The ath11k active pdevs are protected by RCU but the htt pktlog 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: d5c65159 ("ath11k: driver for Qualcomm IEEE 802.11ax devices")
Cc: stable@vger.kernel.org      # 5.6
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20231019112521.2071-1-johan+linaro@kernel.org