igb: fix link reporting when using sgmii

When using sgmii the link was not being properly passed up to the driver
from the underlying link management functions.  This change corrects it so
that get_link_status is cleared when a link has been found.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>