fec_mpc52xx: write in C...

If you need to find a difference between addresses of two
struct members, subtract offsetof() or cast addresses to
char * and subtract those if you prefer it that way.  Doing
that same with s/char */u32/, OTOH...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jeff Garzik <jeff@garzik.org>