sky2: Set SKY2_HW_RAM_BUFFER in sky2_init

The SKY2_HW_RAM_BUFFER bit in hw->flags was checked in sky2_mac_init(),
 before being set later in sky2_up().

Setting SKY2_HW_RAM_BUFFER in sky2_init() where other hw->flags are set
 should avoid this problem recurring.

Signed-off-by: Mike McCormack <mikem@ring3k.org>
Acked-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>