fix EMAC driver for proper napi_synchronize API

The EMAC driver "fix" was merged by mistake before the dust had settled on
the new napi synchronize interface (and before it got merged). The final
version of that function is spelled without underscores.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>