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.