PCI: dwc-plat: Simplify dw_plat_pcie_probe() return values

Save the return value in "ret" for all three cases (DW_PCIE_RC_TYPE,
DW_PCIE_EP_TYPE, default) handled by dw_plat_pcie_probe() and return from a
single place.

[bhelgaas: commit log]
Link: https://lore.kernel.org/r/20220624143428.8334-17-Sergey.Semin@baikalelectronics.ru


Tested-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>