wifi: ath12k: fix OF node refcount imbalance in WSI graph traversal

wifi: ath12k: fix OF node refcount imbalance in WSI graph traversal

ath12k_core_get_wsi_info() traverses the WSI (Wired Serial Interface)
device graph starting from dev->of_node. The current code uses
dev->of_node directly as the local traversal pointer and calls
of_node_put() on error.

Since the driver does not own a reference to dev->of_node, dropping it
during traversal results in the following OF refcount underflow:

OF: ERROR: of_node_release() detected bad of_node_put() on /soc@0/wifi@c000000
CPU: 1 UID: 0 PID: 210 Comm: insmod Not tainted 6.19.0-rc4-next-20260109-00023-g797dd36dc178 #26 PREEMPT
Hardware name: Qualcomm Technologies, Inc. IPQ5332 MI01.2 (DT)
Call trace:
 show_stack+0x18/0x24 (C)
 dump_stack_lvl+0x60/0x80
 dump_stack+0x18/0x24
 of_node_release+0x164/0x1a0
 kobject_put+0xb4/0x278
 of_node_put+0x18/0x28
 ath12k_core_init+0x29c/0x5d4 [ath12k]
 ath12k_ahb_probe+0x950/0xc14 [ath12k]
 platform_probe+0x5c/0xa4
 really_probe+0xc0/0x3ec
 __driver_probe_device+0x80/0x170
 driver_probe_device+0x3c/0x120
 __driver_attach+0xc4/0x218
OF: ERROR: next of_node_put() on this node will result in a kobject warning 'refcount_t: underflow; use-after-free.'

Fix this by explicitly acquiring a reference to the starting node
using of_node_get() and attaching automatic cleanup via
__free(device_node).

Each discovered WSI node is stored in ag->wsi_node[] with its own
of_node_get() reference. These references are later released in
ath12k_core_free_wsi_info() during driver teardown.

Also remove unnecessary memset() of wsi_node array since cleanup now
explicitly sets pointers to NULL.

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.6-01243-QCAHKSWPL_SILICONZ-1
Tested-on: IPQ5332 hw1.0 AHB WLAN.WBE.1.6-01275-QCAHKSWPL_SILICONZ-1

Fixes: 908c10c860e0 ("wifi: ath12k: parse multiple device information from Device Tree")
Signed-off-by: Aaradhana Sahu <aaradhana.sahu@oss.qualcomm.com>
Reviewed-by: Rameshkumar Sundaram <rameshkumar.sundaram@oss.qualcomm.com>
Reviewed-by: Baochen Qiang <baochen.qiang@oss.qualcomm.com>
Link: https://patch.msgid.link/20260410071300.2323603-1-aaradhana.sahu@oss.qualcomm.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>