Fix memory corruption in fec_mpc52xx

The mpc5200 fec driver is corrupting memory. This patch fixes two bugs
where the wrong skb was being referenced.

Signed-off-by: Jon Smirl <jonsmirl@gmail.com>
Acked-by: Domen Puncer <domen.puncer@telargo.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>