PCI: Use PCI_ERROR_RESPONSE to identify config read errors

Include PCI_ERROR_RESPONSE along with 0xFFFF and 0xFFFFFFFF in the comment
about identifying config read errors. This makes checks for config read
errors easier to find. Comment change only.

Link: https://lore.kernel.org/r/866e2db544df45af70df7e64659bf02e03998ae3.1637243717.git.naveennaidu479@gmail.com


Signed-off-by: Naveen Naidu <naveennaidu479@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>