[HAL][KSDK] Fixed ACK/NACK received inverted (https://github.com/mbedmicro/mbed/issues/661)

As reported by Geremia G
(http://developer.mbed.org/forum/bugs-suggestions/topic/5220/)
Merge pull request #684 from Sissors/ksdk

Targets: KSDK - Fix ACK/NACK received inverted (issue #661)