iio: health: max30102: Temperature should be in milli Celsius

As per ABI temperature should be in milli Celsius after scaling,
not Celsius

Note on stable cc.  This driver is breaking the standard IIO
ABI. (JC)

Signed-off-by: Peter Meerwald-Stadler <pmeerw@pmeerw.net>
Acked-by: Matt Ranostay <matt.ranostay@konsulko.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>