PCI: rockchip: Check for pci_scan_root_bus_bridge() failure correctly

pci_scan_root_bus_bridge() returns zero for success, or a negative errno.
A typo in ae13cb9b ("PCI: rockchip: Convert PCI scan API to
pci_scan_root_bus_bridge()") treated zero as a failure.

Fix the typo.

Fixes: ae13cb9b ("PCI: rockchip: Convert PCI scan API to pci_scan_root_bus_bridge()")
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
[bhelgaas: changelog]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>