sys/xtimer.h: fix typo in xtimer_set_msg
sys/xtimer.h: fix typo in xtimer_set_msg

OlegHahm/RIOT,aeneby/RIOT,jasonatran/RIOT,toonst/RIOT,RIOT-OS/RIOT,basilfx/RIOT,OTAkeys/RIOT,kYc0o/RIOT,jasonatran/RIOT,toonst/RIOT,yogo1212/RIOT,RIOT-OS/RIOT,ant9000/RIOT,smlng/RIOT,rfuentess/RIOT,josephnoir/RIOT,toonst/RIOT,yogo1212/RIOT,x3ro/RIOT,kaspar030/RIOT,aeneby/RIOT,smlng/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,ant9000/RIOT,jasonatran/RIOT,basilfx/RIOT,RIOT-OS/RIOT,rfuentess/RIOT,OTAkeys/RIOT,yogo1212/RIOT,kaspar030/RIOT,mtausig/RIOT,aeneby/RIOT,authmillenon/RIOT,rfuentess/RIOT,cladmi/RIOT,mfrey/RIOT,x3ro/RIOT,x3ro/RIOT,yogo1212/RIOT,OTAkeys/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,x3ro/RIOT,OTAkeys/RIOT,mfrey/RIOT,kaspar030/RIOT,cladmi/RIOT,miri64/RIOT,rfuentess/RIOT,jasonatran/RIOT,mtausig/RIOT,kaspar030/RIOT,mfrey/RIOT,yogo1212/RIOT,josephnoir/RIOT,OlegHahm/RIOT,mfrey/RIOT,cladmi/RIOT,cladmi/RIOT,josephnoir/RIOT,x3ro/RIOT,smlng/RIOT,smlng/RIOT,jasonatran/RIOT,aeneby/RIOT,ant9000/RIOT,smlng/RIOT,authmillenon/RIOT,basilfx/RIOT,authmillenon/RIOT,kYc0o/RIOT,OTAkeys/RIOT,miri64/RIOT,OlegHahm/RIOT,ant9000/RIOT,kYc0o/RIOT,basilfx/RIOT,kYc0o/RIOT,rfuentess/RIOT,miri64/RIOT,basilfx/RIOT,authmillenon/RIOT,mtausig/RIOT,ant9000/RIOT,mfrey/RIOT,mtausig/RIOT,kaspar030/RIOT,toonst/RIOT,OlegHahm/RIOT,miri64/RIOT,kYc0o/RIOT,mtausig/RIOT,miri64/RIOT,josephnoir/RIOT,yogo1212/RIOT,authmillenon/RIOT,josephnoir/RIOT,toonst/RIOT,aeneby/RIOT,cladmi/RIOT