modules: hal_nordic: 802.15.4 make possible to disable CSMA-CA

Currently if an attempt to disable CSMA-CA in by setting an
appropriate flag in another (for example application)
CmakeLists.txt it caused lots of warnings. This fix allows
higher level CMakeLists.txt to disable CSMA-CA without
warnings.

Signed-off-by: Artur Hadasz <artur.hadasz@nordicsemi.no>
2 files changed