PCI: imx: Fix probe failure without power domain

On chips without a separate power domain for PCI (such as 6q/6qp) the
imx6_pcie_attach_pd() function incorrectly returns an error.

Fix by returning 0 if dev_pm_domain_attach_by_name() does not find
anything.

Fixes: 3f7cceea ("PCI: imx: Add multi-pd support")
Reported-by: Lukas F.Hartmann <lukas@mntmn.com>
Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
[lorenzo.pieralisi@arm.com: updated commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

drivers/pci/controller/dwc/pci-imx6.c

@@ -310,6 +310,9 @@ static int imx6_pcie_attach_pd(struct device *dev)
 	imx6_pcie->pd_pcie = dev_pm_domain_attach_by_name(dev, "pcie");
 	if (IS_ERR(imx6_pcie->pd_pcie))
 		return PTR_ERR(imx6_pcie->pd_pcie);
+	/* Do nothing when power domain missing */
+	if (!imx6_pcie->pd_pcie)
+		return 0;
 	link = device_link_add(dev, imx6_pcie->pd_pcie,
 			DL_FLAG_STATELESS |
 			DL_FLAG_PM_RUNTIME |