net: Expose some errors generated in net_init

net_init does not always succeed, and there is no existing mechanism to
discover errors. This patch allows callers of net_init (such as net_init)
to handle errors. The root issue is that eth_get_dev can fail, but
net_init_loop doesn't expose that. The ideal way to fix eth_get_dev would
be to return an error with ERR_PTR, but there are a lot of callers, and all
of them just check if it's NULL. Another approach would be to change the
signature to something like

int eth_get_dev(struct udevice **pdev)

but that would require rewriting all of the many callers.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

net/eth-uclass.c

@@ -75,6 +75,9 @@ struct udevice *eth_get_dev(void)
 	struct eth_uclass_priv *uc_priv;
 
 	uc_priv = eth_get_uclass_priv();
+	if (!uc_priv)
+		return NULL;
+
 	if (!uc_priv->current)
 		eth_errno = uclass_first_device(UCLASS_ETH,
 				    &uc_priv->current);