Fix Ethernet init() return codes

Change return values of init() functions in all Ethernet drivers to conform
to the following:

    >=0: Success
    <0:  Failure

All drivers going forward should return 0 on success.  Current drivers that
return 1 on success were left as-is to minimize changes.

Signed-off-by: Ben Warren <biggerbadderben@gmail.com>
Acked-by: Stefan Roese <sr@denx.de>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Acked-by: Kim Phillips <kim.phillips@freescale.com>
Acked-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
Acked-By: Timur Tabi <timur@freescale.com>
diff --git a/net/eth.c b/net/eth.c
index d2fced8..5d9e9c1 100644
--- a/net/eth.c
+++ b/net/eth.c
@@ -433,7 +433,7 @@
 	do {
 		debug ("Trying %s\n", eth_current->name);
 
-		if (!eth_current->init(eth_current,bis)) {
+		if (eth_current->init(eth_current,bis) >= 0) {
 			eth_current->state = ETH_STATE_ACTIVE;
 
 			return 0;