of_address: Guard of_bus_pci_get_flags with CONFIG_PCI

After 2f96593e ("of_address: Add bus type match for pci ranges parser"),
the last user of of_bus_pci_get_flags when CONFIG_PCI is disabled had gone.

This caused unused function warning when compiling without CONFIG_PCI.
Fix by guarding it with CONFIG_PCI.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Fixes: 2f96593e ("of_address: Add bus type match for pci ranges parser")
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>