wifi: ath12k: fix warning on DMA ring capabilities event

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

[ 4153.776040] ath12k_pci 0000:04:00.0: Already processed, so ignoring dma ring caps

This is because ab->num_db_cap is not cleared in
ath12k_wmi_free_dbring_caps(), so clear it to avoid such
warnings.

Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0-03427-QCAHMTSWPL_V1.0_V2.0_SILICONZ-1.15378.4
Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.0.1-00029-QCAHKSWPL_SILICONZ-1
Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20240412060620.27519-5-quic_bqiang@quicinc.com

drivers/net/wireless/ath/ath12k/wmi.c

@@ -4042,6 +4042,7 @@ static void ath12k_wmi_free_dbring_caps(struct ath12k_base *ab)
 {
 	kfree(ab->db_caps);
 	ab->db_caps = NULL;
+	ab->num_db_cap = 0;
 }
 
 static int ath12k_wmi_dma_ring_caps(struct ath12k_base *ab,