net: Fix new EMAC driver for NAPI changes

This fixes the new EMAC driver for the NAPI updates. The previous patch
by Roland Dreier (already applied) to do that doesn't actually work. This
applies on top of it makes it work on my test Ebony machine.

This patch depends on "net: Add __napi_sycnhronize() to sync with napi poll"
posted previously.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>