radio/nrf802154: fix set_cca_threshold range
radio/nrf802154: fix set_cca_threshold range

This commit fixes the CCA threshold range for set_cca_threshold.
Without this commit the threshold overflows when using values below
the receiver sensitivity.

RIOT-OS/RIOT,miri64/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,OTAkeys/RIOT,jasonatran/RIOT,kaspar030/RIOT,OlegHahm/RIOT,miri64/RIOT,jasonatran/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,authmillenon/RIOT,ant9000/RIOT,authmillenon/RIOT,kaspar030/RIOT,kYc0o/RIOT,kaspar030/RIOT,ant9000/RIOT,OlegHahm/RIOT,miri64/RIOT,kYc0o/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,jasonatran/RIOT,kYc0o/RIOT,ant9000/RIOT,OlegHahm/RIOT,ant9000/RIOT,OTAkeys/RIOT,miri64/RIOT,authmillenon/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,authmillenon/RIOT,authmillenon/RIOT,authmillenon/RIOT,OlegHahm/RIOT,miri64/RIOT,ant9000/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,kaspar030/RIOT