hwmon: (f71882fg) Fix negative temperature

All temperature of Fintek superio hwmonitor that using 1-byte reg will use
2's complement.

In show_temp()
temp = data->temp[nr] * 1000;

When data->temp[nr] read as 255, it indicate -1C, but this code will report
255C to userspace. It'll be ok when change to:
temp = ((s8)data->temp[nr]) * 1000;

Signed-off-by: Ji-Ze Hong (Peter Hong) <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Guenter Roeck <[e-mail]>

drivers/hwmon/f71882fg.c

···
 		temp *= 125;
 		if (sign)
 			temp -= 128000;
-	} else
-		temp = data->temp[nr] * 1000;
+	} else {
+		temp = ((s8)data->temp[nr]) * 1000;
+	}
 
 	return sprintf(buf, "%d\n", temp);
 }