wifi: rtw89: pass chan to rfk_band_changed()

Originally, all chips have implemented rfk_band_changed() and access chan
with hard-code RTW89_CHANCTX_0 in it. But, it's problematic when the chip
supports multiple channels.

So, change the prototype of rfk_band_changed() and pass chan ahead. And,
we will refine the implementation of each chip in the following.

Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20240819091724.33730-2-pkshih@realtek.com