qcacmn: add pdev NULL check in peer inactivity timer

In dp_txrx_peer_find_inact_timeout_handler ignore pdev
which is already detached

Change-Id: I0349d5f9c8d249cf332727bff3c120ddf38a6807
CRs-fixed: 2312279

dp/wifi3.0/dp_main.c

@@ -2699,6 +2699,8 @@ static os_timer_func(dp_txrx_peer_find_inact_timeout_handler)
 
 	for (i = 0; i < soc->pdev_count; i++) {
 	pdev = soc->pdev_list[i];
+	if (!pdev)
+		continue;
 	qdf_spin_lock_bh(&pdev->vdev_list_lock);
 	TAILQ_FOREACH(vdev, &pdev->vdev_list, vdev_list_elem) {
 		if (vdev->opmode != wlan_op_mode_ap)