sh_eth: Do not print an error message for probe deferral

EPROBE_DEFER is not an error, hence printing an error message like

    sh-eth ee700000.ethernet: failed to initialise MDIO

may confuse the user.

To fix this, suppress the error message in case of probe deferral.
While at it, shorten the message, and add the actual error code.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: David S. Miller <davem@davemloft.net>