igb: fix EEH recovery during reset on PPC

EEH is not recovering in a reasonable amount of time on PPC during
igb_down().

Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>