rtw88: coex: change the decode method from firmware

Fix sometimes FW information will be parsed as wrong value,
do a correction of sign bit to show the correct information.
(Ex, Value should be 20, but it shows 236.)
Signed-off-by: Ching-Te Ku <ku920601@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201112031430.4846-12-pkshih@realtek.com

drivers/net/wireless/realtek/rtw88/coex.c

@@ -2882,7 +2882,7 @@ void rtw_coex_wl_fwdbginfo_notify(struct rtw_dev *rtwdev, u8 *buf, u8 length)
 		if (buf[i] >= val)
 			coex_stat->wl_fw_dbg_info[i] = buf[i] - val;
 		else
-			coex_stat->wl_fw_dbg_info[i] = val - buf[i];
+			coex_stat->wl_fw_dbg_info[i] = 255 - val + buf[i];
 
 		coex_stat->wl_fw_dbg_info_pre[i] = buf[i];
 	}