net: ethernet: mv643xx: Fix over zealous checking of_get_mac_address()

There is often not a MAC address available in an EEPROM accessible by
Linux with Marvell devices. Instead the bootload has the MAC address
and directly programs it into the hardware. So don't consider an error
from of_get_mac_address() has fatal. However, the check was added for
the case where there is a MAC address in an the EEPROM, but the EEPROM
has not probed yet, and -EPROBE_DEFER is returned. In that case the
error should be returned. So make the check specific to this error
code.

Cc: Mauri Sandberg <maukka@ext.kapsi.fi>
Reported-by: Thomas Walther <walther-it@gmx.de>
Fixes: 42404d8f ("net: mv643xx_eth: process retval from of_get_mac_address")
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20220405000404.3374734-1-andrew@lunn.chSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/marvell/mv643xx_eth.c

@@ -2751,7 +2751,7 @@ static int mv643xx_eth_shared_of_add_port(struct platform_device *pdev,
 	}
 
 	ret = of_get_mac_address(pnp, ppd.mac_addr);
-	if (ret)
+	if (ret == -EPROBE_DEFER)
 		return ret;
 
 	mv643xx_eth_property(pnp, "tx-queue-size", ppd.tx_queue_size);