iio: pressure: bmp280: Fix BMP580 temperature reading

Fix overflow issue when storing BMP580 temperature reading and
properly preserve sign of 24-bit data.

Signed-off-by: Adam Rizkalla <ajarizzo@gmail.com>
Tested-By: Vasileios Amoiridis <vassilisamir@gmail.com>
Acked-by: Angel Iglesias <ang.iglesiasg@gmail.com>
Link: https://lore.kernel.org/r/Zin2udkXRD0+GrML@adam-asahi.lan
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/pressure/bmp280-core.c

@@ -1394,12 +1394,12 @@ static int bmp580_read_temp(struct bmp280_data *data, int *val, int *val2)
 
 	/*
 	 * Temperature is returned in Celsius degrees in fractional
-	 * form down 2^16. We rescale by x1000 to return milli Celsius
-	 * to respect IIO ABI.
+	 * form down 2^16. We rescale by x1000 to return millidegrees
+	 * Celsius to respect IIO ABI.
 	 */
-	*val = raw_temp * 1000;
-	*val2 = 16;
-	return IIO_VAL_FRACTIONAL_LOG2;
+	raw_temp = sign_extend32(raw_temp, 23);
+	*val = ((s64)raw_temp * 1000) / (1 << 16);
+	return IIO_VAL_INT;
 }
 
 static int bmp580_read_press(struct bmp280_data *data, int *val, int *val2)