sh_eth: kill 'ret' variable in sh_eth_ring_init()

The 'ret' local variable in sh_eth_ring_init() serves no useful purpose as
the only  values it gets assigned are 0 and -ENOMEM both of which could be
returned directly...

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>