net: samsung: sxgbe: Make sxgbe_drv_remove() return void

sxgbe_drv_remove() returned zero unconditionally, so it can be converted
to return void without losing anything. The upside is that it becomes
more obvious in its callers that there is no error to handle.

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>