net: fec: using the standard return codes when xdp xmit errors

This patch standardizes the inconsistent return values for unsuccessful
XDP transmits by using standardized error codes (-EBUSY or -ENOMEM).

Signed-off-by: Shenwei Wang <shenwei.wang@nxp.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>