cpu/stm32/periph_can: use container_of()
cpu/stm32/periph_can: use container_of()

This silences false positives of -Wcast-align

kaspar030/RIOT,kYc0o/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,miri64/RIOT,ant9000/RIOT,OlegHahm/RIOT,kYc0o/RIOT,kaspar030/RIOT,ant9000/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,ant9000/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,ant9000/RIOT,RIOT-OS/RIOT,miri64/RIOT,jasonatran/RIOT,OlegHahm/RIOT,miri64/RIOT,RIOT-OS/RIOT,ant9000/RIOT,jasonatran/RIOT,miri64/RIOT,jasonatran/RIOT,kaspar030/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,kaspar030/RIOT,jasonatran/RIOT,miri64/RIOT,kaspar030/RIOT