PCI: kirin: Fix reset gpio name

As documented in the devicetree bindings (pci/kirin-pcie.txt) and the
reset gpio name must be 'reset-gpios'. However, current driver
erroneously looks for a 'reset-gpio' resource which makes the driver
probe fail. Fix it.

Fixes: fc5165db ("PCI: kirin: Add HiSilicon Kirin SoC PCIe controller driver")
Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
[lorenzo.pieralisi@arm.com: updated the commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Xiaowei Song <songxiaowei@hisilicon.com>