fs_enet: Fix SCC Ethernet on CPM2, and crash in fs_enet_rx_napi()

Signed-off-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Vitaly Bordug <vitb@kernel.crashing.org>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>