iio: pressure: bmp280: fix temp compensation

Temperature reads on bmp280 device always return 0,
due to a missing step in the compensation formula
(data->tfine is never initialized).

Initialize data->tfine value so we get correct
temperature and pressure values.

Signed-off-by: Irina Tirdea <irina.tirdea@intel.com>
Reviewed-by: Vlad Dogaru <vlad.dogaru@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/pressure/bmp280.c

@@ -172,6 +172,7 @@ static s32 bmp280_compensate_temp(struct bmp280_data *data,
 	var2 = (((((adc_temp >> 4) - ((s32)le16_to_cpu(buf[T1]))) *
 		  ((adc_temp >> 4) - ((s32)le16_to_cpu(buf[T1])))) >> 12) *
 		((s32)(s16)le16_to_cpu(buf[T3]))) >> 14;
+	data->t_fine = var1 + var2;
 
 	return (data->t_fine * 5 + 128) >> 8;
 }