Update MPL3115A2.ino

For projects that require instantaneous read limited only by the sensor's OverSampleRate, you must set FIFO mode (in the F_SETUP register) to non-zero and toggle the OST bit (in the CTRL_REG1 register) to 1.

Changes were made in the main read() functions as well, as the break loop didn't break out of anything -- the code below it was still running even when no new data was available for acquisition.