endTransmission returns number of bytes written instead of status on Arduino Due

[Lauszus]

There is a bug in the Sam implementation of Wire.endTransmission.
It returns the number of bytes written + 1: https://github.com/arduino/Arduino/blob/ide-1.5.x/hardware/arduino/sam/libraries/Wire/Wire.cpp#L177-L194 and not the status: http://arduino.cc/en/Reference/WireEndTransmission, as in the AVR implementation: https://github.com/arduino/Arduino/blob/ide-1.5.x/hardware/arduino/avr/libraries/Wire/Wire.cpp#L137-L147.

[cmaglie]

Fixed by #1994