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: NIrina Tirdea <irina.tirdea@intel.com>
Reviewed-by: NVlad Dogaru <vlad.dogaru@intel.com>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>