[BNX2]: Fix Serdes WoL bug.

The bug is in the code in bnx2_set_power_state() that assumes copper
devices when setting up WoL.  This is no longer true after adding WoL
support for Serdes devices.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>