net: arc: Make arc_emac_remove() return void

The function returns zero unconditionally. Change it to return void instead
which simplifies its callers as error handing becomes unnecessary.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>