wifi: ath12k: Refactor the mac80211 hw access from link/radio

Currently, mac80211 hardware accesses link/radio structure directly in
multiple locations. Introduce helper function to avoid this direct
access, as this change will facilitate refactoring for Multi-link
operation support.

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.0.1-00029-QCAHKSWPL_SILICONZ-1
Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3

Signed-off-by: Karthikeyan Periyasamy <quic_periyasa@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20240118010320.3918136-2-quic_periyasa@quicinc.com