PCI: of: Reduce missing non-prefetchable memory region to a warning

The pci-rcar-gen2 controller requires only a prefetchable memory region,
and the error prevents using pci_parse_request_of_pci_ranges() for it.
Let's reduce this to just a warning message so this function can be used
for pci-rcar-gen2.

Link: https://lore.kernel.org/r/20200722022514.1283916-17-robh@kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

drivers/pci/of.c

@@ -564,11 +564,10 @@ int pci_parse_request_of_pci_ranges(struct device *dev,
  }
  }
 
- if (res_valid)
- return 0;
+ if (!res_valid)
+ dev_warn(dev, "non-prefetchable memory resource required\n");
 
- dev_err(dev, "non-prefetchable memory resource required\n");
- err = -EINVAL;
+ return 0;
 
  out_release_res:
  pci_free_resource_list(resources);