igb: return PCI_ERS_RESULT_DISCONNECT on permanent error

PCI drivers that implement the io_error_detected callback should return
PCI_ERS_RESULT_DISCONNECT if the state passed in is
pci_channel_io_perm_failure.  This patch fixes the issue for igb.

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>