wifi: ath12k: Avoid NULL pointer access during management transmit cleanup

Currently 'ar' reference is not added in skb_cb.
Though this is generally not used during transmit completion
callbacks, on interface removal the remaining idr cleanup callback
uses the ar pointer from skb_cb from management txmgmt_idr. Hence fill them
during transmit call for proper usage to avoid NULL pointer dereference.

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.0.1-00029-QCAHKSWPL_SILICONZ-1

Signed-off-by: Balamurugan S <quic_bselvara@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20230518071046.14337-1-quic_bselvara@quicinc.com