net: sgi: ioc3-eth: get rid of ioc3_clean_rx_ring()

Move clearing of the descriptor valid bit into ioc3_alloc_rings. This
makes ioc3_clean_rx_ring obsolete.

Signed-off-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>