wifi: rtw89: fw: correct chan access in assoc_cmac_tbl_g7 and update_beacon_be

Originally, these H2C commands access chan with hard-code RTW89_CHANCTX_0.
They are problematic when the chip supports multiple channels. So, correct
them by accessing right chan under rtwvif.

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20240727080650.12195-7-pkshih@realtek.com