e100: Fix MDIO/MDIO-X

MDIO/MDIO-X was broken due to a wrong errata. Removing the workaround
code fixes for affected NICs.

Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>