wifi: ath11k: consistently use ath11k_mac_get_fw_stats()

wifi: ath11k: consistently use ath11k_mac_get_fw_stats()

Currently to get firmware stats, ath11k_mac_op_get_txpower() calls
ath11k_fw_stats_request() and ath11k_mac_op_sta_statistics() calls
ath11k_mac_get_fw_stats(). Those two helpers are basically doing
the same, except for:

1. ath11k_mac_get_fw_stats() verifies ar->state inside itself.
2. ath11k_mac_get_fw_stats() calls ath11k_mac_fw_stats_request()
   which then calls ath11k_mac_fw_stats_reset() to free pdev/vdev
   stats whereas only pdev stats are freed by ath11k_fw_stats_request().
3. ath11k_mac_get_fw_stats() waits for ar->fw_stats_complete and
   ar->fw_stats_done, whereas ath11k_fw_stats_request() only waits for
   ar->fw_stats_complete.

Change to call ath11k_mac_get_fw_stats() in ath11k_mac_op_get_txpower().
This is valid because:

1. ath11k_mac_op_get_txpower() also has the same request on ar->state.
2. it is harmless to call ath11k_fw_stats_vdevs_free() since
   ar->fw_stats.vdevs should be empty and there should be no one
   expecting it at that time.
3. ath11k_mac_op_get_txpower() only needs pdev stats. For pdev stats,
   ar->fw_stats_done is set to true whenever ar->fw_stats_complete is
   set to true in ath11k_update_stats_event(). So additional wait on
   ar->fw_stats_done does not wast any time.

Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3.6510.37

Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
Reviewed-by: Vasanthakumar Thiagarajan <vasanthakumar.thiagarajan@oss.qualcomm.com>
Link: https://patch.msgid.link/20250220082448.31039-8-quic_bqiang@quicinc.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>