Update getChromaticityCoordinate.ino

The starting block to read must have the same direction that the green color(first color).
A Low-Cost Real Color Picker Based on Arduino version

Code fixed in order to do this work:
Agudo, J.E.; Pardo, P.J.; Sánchez, H.; Pérez, Á.L.; Suero, M.I. A Low-Cost Real Color Picker Based on Arduino. Sensors 2014, 14, 11943-11956. http://www.mdpi.com/1424-8220/14/7/11943
Merge pull request #2 from jeagudo/master

The REG_BLOCK_READ and REG_GREEN_LOW direction must be the same