backports: handle pci_error_handlers change to const

backports: handle pci_error_handlers change to const

In kernel 3.7 struct pci_driver changed pci_error_handlers to const.
Address this by putting ifdef around the code.

commit 494530284f16298050ab99f54b7b12dd7d1418a1
Author: Stephen Hemminger <shemminger@vyatta.com>
Date:   Fri Sep 7 09:33:14 2012 -0700

    PCI: Make pci_error_handlers const

git describe --contains 494530284f16298050ab99f54b7b12dd7d1418a1
v3.7-rc1~177^2~9^2~3

Signed-off-by: Stefan Assmann <sassmann@kpanic.de>
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>