Several schema warnings are seen when running:

make dtbs_check DT_SCHEMA_FILES=pci-bus.yaml

Fix them.
Signed-off-by: Fabio Estevam <festevam@denx.de>
Acked-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>