bcm63xx_enet: remove redundant variable definitions

in this function,‘ret’ is always assigned,so this's definition
'ret = 0' make no sense.

Signed-off-by: tangbin <tangbin@cmss.chinamobile.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>