wifi: ath11k: Fix race condition with struct htt_ppdu_stats_info

A crash happens when running the traffic with multiple clients:

Crash Signature : Unable to handle kernel paging request at
virtual address ffffffd700970918 During the crash, PC points to
"ieee80211_tx_rate_update+0x30/0x68 [mac80211]"
LR points to "ath11k_dp_htt_htc_t2h_msg_handler+0x5a8/0x8a0 [ath11k]".

Struct ppdu_stats_info is allocated and accessed from event callback via copy
engine tasklet, this has a problem when freeing it from ath11k_mac_op_stop().

Use data_lock during entire ath11k_dp_htt_get_ppdu_desc() call to protect
struct htt_ppdu_stats_info access and to avoid race condition when accessing it
from ath11k_mac_op_stop().

Tested-on: IPQ8074 hw2.0 AHB WLAN.HK.2.7.0.1-01744-QCAHKSWPL_SILICONZ-1

Signed-off-by: Govindaraj Saminathan <quic_gsaminat@quicinc.com>
Co-developed-by: Karthikeyan Kathirvel <quic_kathirve@quicinc.com>
Signed-off-by: Karthikeyan Kathirvel <quic_kathirve@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20221124071104.22506-1-quic_kathirve@quicinc.com