wifi: ath12k: change to treat alpha code na as world wide regdomain

wifi: ath12k: change to treat alpha code na as world wide regdomain

Some firmware versions for WCN7850 report the default regdomain with
alpha code "na" by default when load as a world wide regdomain,
ath12k should treat it as a world wide alpha code.

Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0-03427-QCAHMTSWPL_V1.0_V2.0_SILICONZ-1.15378.4

Signed-off-by: Wen Gong <quic_wgong@quicinc.com>
Acked-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20230906090355.19181-1-quic_wgong@quicinc.com