drivers/ws281x: improve documentation
drivers/ws281x: improve documentation

Replace 'to' with 'too' and remove the space between '8 MHz'.

Signed-off-by: Yegor Yefremov <379041fa42359f10443de1f461b1b247ec449fae@googlemail.com>

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