rtw89: Limit the CFO boundaries of x'tal value

Set the boundaries of x'tal value to avoid extremely adjusted results,
causing severely unexpected CFO.

Signed-off-by: Yi-Tang Chiu <chiuyitang@realtek.com>
Signed-off-by: Yuan-Han Zhang <yuanhan1020@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/20220218034537.9338-1-pkshih@realtek.com