wifi: rtw89: chan: concentrate the logic of setting/clearing chanctx bitmap

Originally, the logic for setting bits was wrapped inside the configuring
function. However, raw clearing bits, clear_bit, was called directly. To be
more paired and more understandable. Concentrate the logic of them into the
same function.

(don't change logic at all)

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20250605114207.12381-2-pkshih@realtek.com