tg3: Add higher cpu clock for 5762.

This patch has fix for TX timeout while running bi-directional
traffic with 100 Mbps using 5762.

Signed-off-by: Sanjeev Bansal <sanjeevb.bansal@broadcom.com>
Signed-off-by: Siva Reddy Kallam <siva.kallam@broadcom.com>
Reviewed-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>