net: macb: call pm_runtime_put_sync on failure path

Call pm_runtime_put_sync() on failure path of at91ether_open.

Fixes: e6a41c23

 ("net: macb: ensure interface is not suspended on at91rm9200")
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>