make/riscv: remove use of export for LINKFLAGS
make/riscv: remove use of export for LINKFLAGS

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