wifi: rtw89: sar: let caller decide the center frequency to query

If multiple channels, SAR will be hard to determine the center frequency
to query. Therefore, we move this decision out of SAR.

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230816082133.57474-4-pkshih@realtek.com