successful multibyte write, and multibyte read to/from ofsx registers.
need to improve i2c code seperation, and refine i2c functions - its just
messy around the multi byte read and write functions, and the repeated
start function. take care of I2C_AcknowledgeConfig(I2Cx,ENABLE/DISABLE)
as this was the issue with nack being sent too early. default config is
disabled. perhaps should be enabled by default.