sys/flashwrite: remove useless line
sys/flashwrite: remove useless line

scan-build reported: Value stored to 'flashpage_pos' is never read

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