dm9000: Return an ERR_PTR() in all error conditions of dm9000_parse_dt()

In one error condition dm9000_parse_dt() returns NULL, however the
return value is checked using IS_ERR() in dm9000_probe(), leading to the
error not being properly propagated if CONFIG_OF is not enabled or the
device tree data is not available. Fix this by also returning an
ERR_PTR() in this case.

Fixes: 0b8bf1ba (net: dm9000: Allow instantiation using device tree)
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/davicom/dm9000.c

@@ -1399,7 +1399,7 @@ static struct dm9000_plat_data *dm9000_parse_dt(struct device *dev)
 	const void *mac_addr;
 
 	if (!IS_ENABLED(CONFIG_OF) || !np)
-		return NULL;
+		return ERR_PTR(-ENXIO);
 
 	pdata = devm_kzalloc(dev, sizeof(*pdata), GFP_KERNEL);
 	if (!pdata)