tg3: Remove SPEED_UNKNOWN checks

tg3: Remove SPEED_UNKNOWN checks

tg3_phy_copper_begin() has code that configures the link
advertisements through the use of the link_config.speed and
link_config.duplex members.  The driver does not internally use these
members in this way, nor is it (currently) permitted via the ethtool
interface.  This patch removes the dead code.

(cherry picked from commit d13ba512cbba7de5d55d7a3b2aae7d83c8921457)
Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Joe Jin <joe.jin@oracle.com>