iio temperature/mlx90632: silence a static checker warning

This shouldn't affect runtime at all, but Smatch complains that we
should check if mlx90632_read_ambient_raw() otherwise we
"ambient_new_raw" can be uninitialized.

    drivers/iio/temperature/mlx90632.c:509 mlx90632_calc_ambient_dsp105()
    error: uninitialized symbol 'ambient_new_raw'.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Crt Mori <cmo@melexis.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/temperature/mlx90632.c

@@ -506,6 +506,8 @@ static int mlx90632_calc_ambient_dsp105(struct mlx90632_data *data, int *val)
 
 	ret = mlx90632_read_ambient_raw(data->regmap, &ambient_new_raw,
 					&ambient_old_raw);
+	if (ret < 0)
+		return ret;
 	*val = mlx90632_calc_temp_ambient(ambient_new_raw, ambient_old_raw,
 					  PT, PR, PG, PO, Gb);
 	return ret;