PCI: brcmstb: Assign pcie->gen from of_pci_get_max_link_speed()

After commit 03f9209 ("PCI: controller: Validate max-link-speed"),
pcie->gen stopped being assigned and as a result the established PCIe link
would stop supporting Gen3 speeds on 2712 since pcie->gen is used to
populate LnkCntl2 and LnkCap in brcm_pcie_set_gen().

If the 'max-link-speed' property is not specified, or it exceeds Gen3,
resort to the HW defaults.

Link: raspberrypi/linux#7343
Reported-by: Dom Cobley <popcornmix@gmail.com>
Reported-by: Phil Elwell <phil@raspberrypi.com>
Fixes: 03f9209 ("PCI: controller: Validate max-link-speed")
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Hans Zhang <18255117159@163.com>
Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>
Link: https://patch.msgid.link/20260506164537.103196-1-florian.fainelli@broadcom.com

Author: ffainelli

drivers/pci/controller/pcie-brcmstb.c

@@ -2072,8 +2072,10 @@ static int brcm_pcie_probe(struct platform_device *pdev)
 		return PTR_ERR(pcie->clk);
 
 	ret = of_pci_get_max_link_speed(np);
-	if (pcie_get_link_speed(ret) == PCI_SPEED_UNKNOWN)
+	if (ret < 0 || ret > 3)
 		pcie->gen = 0;
+	else
+		pcie->gen = ret;
 
 	pcie->ssc = of_property_read_bool(np, "brcm,enable-ssc");