PCI: Correct error reporting with PCIe failed link retraining

Only return successful completion status from pcie_failed_link_retrain() if
retraining has actually been done, preventing excessive delays from being
triggered at call sites in a hope that communication will finally be
established with the downstream device where in fact nothing has been done
about the link in question that would justify such a hope.

Fixes: a89c8224 ("PCI: Work around PCIe link training failures")
Link: https://lore.kernel.org/r/alpine.DEB.2.21.2408091133260.61955@angie.orcam.me.uk


Reported-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/aa2d1c4e-9961-d54a-00c7-ddf8e858a9b0@linux.intel.com/


Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Cc: <stable@vger.kernel.org> # v6.5+