wifi: rtw89: correct the DCFO tracking flow to improve CFO compensation

DCFO tracking compensate the CFO (carrier frequency offset) by digital
hardware that provides fine CFO estimation. Although the avg_cfo which
is a coarse information becomes zero, still we need DCFO tracking to
compensate the residual CFO. However, the original flow skips the case
when avg_cfo is zero, so we fix it to have expected performance.

Signed-off-by: Cheng-Chieh Hsieh <cj.hsieh@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/20231016065115.751662-5-pkshih@realtek.com