drivers/mcp2515: use container_of()
drivers/mcp2515: use container_of()

This silences false positives of -Wcast-align

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