PCI: keystone: Fix NULL pointer dereference in case of DT error in ks_pcie_setup_rc_app_regs()

In the Linux kernel, the following vulnerability has been resolved: PCI: keystone: Fix NULL pointer dereference in case of DT error in ks_pcie_setup_rc_app_regs() If IORESOURCE_MEM is not provided in Device Tree due to any error, resource_list_first_type() will return NULL and pci_parse_request_of_pci_ranges() will just emit a warning. This will cause a NULL pointer dereference. Fix this bug by adding NULL return check. Found by Linux Verification Center (linuxtesting.org) with SVACE.