net: Change return codes from net/eth.c to use errorno constants

Many functions returned -1 previously. Change them to return appropriate error
codes.
Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Reported-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>

net/eth.c

@@ -227,7 +227,7 @@ int eth_unregister(struct eth_device *dev)
 
 	/* No device */
 	if (!eth_devices)
-		return -1;
+		return -ENODEV;
 
 	for (cur = eth_devices; cur->next != eth_devices && cur->next != dev;
 	     cur = cur->next)
@@ -235,7 +235,7 @@ int eth_unregister(struct eth_device *dev)
 
 	/* Device not found */
 	if (cur->next != dev)
-		return -1;
+		return -ENODEV;
 
 	cur->next = dev->next;
 
@@ -368,7 +368,7 @@ int eth_init(bd_t *bis)
 
 	if (!eth_current) {
 		puts("No ethernet found.\n");
-		return -1;
+		return -ENODEV;
 	}
 
 	/* Sync environment with network devices */
@@ -397,7 +397,7 @@ int eth_init(bd_t *bis)
 		eth_try_another(0);
 	} while (old_current != eth_current);
 
-	return -1;
+	return -ETIMEDOUT;
 }
 
 void eth_halt(void)
@@ -413,7 +413,7 @@ void eth_halt(void)
 int eth_send(void *packet, int length)
 {
 	if (!eth_current)
-		return -1;
+		return -ENODEV;
 
 	return eth_current->send(eth_current, packet, length);
 }
@@ -421,7 +421,7 @@ int eth_send(void *packet, int length)
 int eth_rx(void)
 {
 	if (!eth_current)
-		return -1;
+		return -ENODEV;
 
 	return eth_current->recv(eth_current);
 }