PCI: tegra194: Use devm_gpiod_get_optional() to parse "nvidia,refclk-select"

PCI: tegra194: Use devm_gpiod_get_optional() to parse "nvidia,refclk-select"

The GPIO DT property "nvidia,refclk-select", to select the PCIe reference
clock is optional. Use devm_gpiod_get_optional() to get it.

Fixes: c57247f940e8 ("PCI: tegra: Add support for PCIe endpoint mode in Tegra194")
Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
Signed-off-by: Manikanta Maddireddy <mmaddireddy@nvidia.com>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Jon Hunter <jonathanh@nvidia.com>
Reviewed-by: Jon Hunter <jonathanh@nvidia.com>
Reviewed-by: Vidya Sagar <vidyas@nvidia.com>
Link: https://patch.msgid.link/20260324190755.1094879-7-mmaddireddy@nvidia.com