wifi: ath11k: fix warning on DMA ring capabilities event

We are seeing below warning in both reset and suspend/resume scenarios:

[69663.691847] ath11k_pci 0000:02:00.0: Already processed, so ignoring dma ring caps

This is because ab->num_db_cap is not cleared in
ath11k_wmi_free_dbring_caps(), so clear it to avoid such
warnings.

Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3.6510.30
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
Link: https://msgid.link/20240221024725.10057-5-quic_bqiang@quicinc.com

drivers/net/wireless/ath/ath11k/wmi.c

 // SPDX-License-Identifier: BSD-3-Clause-Clear
 /*
  * Copyright (c) 2018-2019 The Linux Foundation. All rights reserved.
- * Copyright (c) 2021-2023 Qualcomm Innovation Center, Inc. All rights reserved.
+ * Copyright (c) 2021-2024 Qualcomm Innovation Center, Inc. All rights reserved.
  */
 #include <linux/skbuff.h>
 #include <linux/ctype.h>
@@ -4857,6 +4857,7 @@ static void ath11k_wmi_free_dbring_caps(struct ath11k_base *ab)
 {
 	kfree(ab->db_caps);
 	ab->db_caps = NULL;
+	ab->num_db_cap = 0;
 }
 
 static int ath11k_wmi_tlv_dma_ring_caps(struct ath11k_base *ab,