wifi: ath12k: fix NULL access in assign channel context handler

wifi: ath12k: fix NULL access in assign channel context handler

Currently, when ath12k_mac_assign_vif_to_vdev() fails, the radio handle
(ar) gets accessed from the link VIF handle (arvif) for debug logging, This
is incorrect. In the fail scenario, radio handle is NULL. Fix the NULL
access, avoid radio handle access by moving to the hardware debug logging
helper function (ath12k_hw_warn).

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.3.1-00173-QCAHKSWPL_SILICONZ-1
Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3

Fixes: 90570ba4610b ("wifi: ath12k: do not return invalid link id for scan link")
Reviewed-by: Vasanthakumar Thiagarajan <vasanthakumar.thiagarajan@oss.qualcomm.com>
Signed-off-by: Karthikeyan Periyasamy <quic_periyasa@quicinc.com>
Link: https://patch.msgid.link/20250324062518.2752822-8-quic_periyasa@quicinc.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>