PCI: kirin: Return -EPROBE_DEFER in case the gpio isn't ready

PCI: kirin: Return -EPROBE_DEFER in case the gpio isn't ready

PCI host bridge driver can be probed before the gpiochip it requires,
so, of_get_named_gpio() can return -EPROBE_DEFER. Current code lets the
kirin_pcie_probe() directly return -ENODEV, which results in the PCI
host controller driver probe failure; with this error code the PCI host
controller driver will not be probed again when the gpiochip driver is
loaded.

Fix the above issue by letting kirin_pcie_probe() return -EPROBE_DEFER in
such a case.

Link: https://lore.kernel.org/r/20200918123800.19983-1-huobean@gmail.com
Signed-off-by: Bean Huo <beanhuo@micron.com>
[lorenzo.pieralisi@arm.com: commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>