NET: fec: only enable napi if we are successful

If napi is left enabled after a failed attempt to bring the interface
up, we BUG:

fec 2188000.ethernet eth0: no PHY, assuming direct connection to switch
libphy: PHY fixed-0:00 not found
fec 2188000.ethernet eth0: could not attach to PHY
------------[ cut here ]------------
kernel BUG at include/linux/netdevice.h:502!
Internal error: Oops - BUG: 0 [#1] SMP ARM
...
PC is at fec_enet_open+0x4d0/0x500
LR is at __dev_open+0xa4/0xfc

Only enable napi after we are past all the failure paths.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/fec_main.c

@@ -1778,8 +1778,6 @@ fec_enet_open(struct net_device *ndev)
 	struct fec_enet_private *fep = netdev_priv(ndev);
 	int ret;
 
-	napi_enable(&fep->napi);
-
 	/* I should reset the ring buffers here, but I don't yet know
 	 * a simple way to do that.
 	 */
@@ -1794,6 +1792,8 @@ fec_enet_open(struct net_device *ndev)
 		fec_enet_free_buffers(ndev);
 		return ret;
 	}
+
+	napi_enable(&fep->napi);
 	phy_start(fep->phy_dev);
 	netif_start_queue(ndev);
 	fep->opened = 1;