wifi: ath11k: refactor setting country code logic

ath11k_wmi_send_set_current_country_cmd() is called in several places
and all of them are just simply repeating the same logic.

Refactor to make code clean.

Compile tested only.

Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20240520024148.5472-2-quic_bqiang@quicinc.com