Check TLP packet successful completion status. This fix the issue when
accessing multi-function devices in enumeration process, TLP will return
error when accessing non-exist function number. Returns PCI error code
instead of generic errno.
Tested on Ethernet adapter card with multi-functions.
[bhelgaas: simplify completion status checking code] Signed-off-by: Ley Foon Tan <lftan@altera.com> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>