rcar_pcie_parse_request_of_pci_ranges() can fail and return an error
code, but this is not checked nor handled.

Fix this by adding the missing error handling.

Fixes: 5d2917d4 ("PCI: rcar: Convert to DT resource parsing API")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>