bnx2x: Fix LED blink rate for 578xx

Adjust blink rate on 578xx to fit its clock rate.

Signed-off-by: Yaniv Rosner <yanivr@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>