drivers/kw41zrf: fix wrong endianness in short_addr get/set
drivers/kw41zrf: fix wrong endianness in short_addr get/set

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