PCI: Fix pci-e port driver slot_reset bad default return value

When an upstream port reports an AER error to root port, kernel
starts error recovery procedures. The default return value of
function pcie_portdrv_slot_reset is PCI_ERS_RESULT_NONE. If all
port service drivers of the downstream port under the upstream
port have no slot_reset method in pci_error_handlers, AER recovery
would stop without resume. Below patch against 2.6.30-rc3 fixes it.

Signed-off-by: Zhang Yanmin <yanmin.zhang@linux.intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>