wifi: rtw89: add suffix "_ax" to Wi-Fi 6 HW scan struct and func

These stuffs have no suffix, but not universal, and only work for Wi-Fi 6.
Since the corresponding HW scan struct/func of Wi-Fi 7 have suffix "_be",
to avoid misunderstanding and improve readability, also add suffix "_ax"
to these Wi-Fi 6 stuffs.

(No logic is changed.)

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20250422014620.18421-4-pkshih@realtek.com