MIPS: Use !pci_is_root_bus(bus) in ops-bridge.c

MIPS: Use !pci_is_root_bus(bus) in ops-bridge.c

This is a manual cherrypick of commit c7ddc3d137b7 from Alastair
Bridgewater's IP35 tree that replaces two cases of
"if (bus->number > 0)" with a more correct "if (!pci_is_root_bus(bus))"
in arch/mips/pci/ops-bridge.c.

Cc: linux-mips@linux-mips.org
Cc: Alastair Bridgewater <alastair.bridgewater@gmail.com>
Suggested-by: Alastair Bridgewater <alastair.bridgewater@gmail.com>
Signed-off-by: Joshua Kinard <kumba@gentoo.org>
Patchwork: https://patchwork.linux-mips.org/patch/17501/
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Linux/MIPS <linux-mips@linux-mips.org>