dm: pci: change bus number register setting compliant with Linux

This patch is to change U-Boot PCI bus assignement compliant with Linux.
It means each PCIe controller's bus number is 0, not the current maximum
PCI bus number, when start to scan this controller.

Signed-off-by: Minghuan Lian <Minghuan.Lian@nxp.com>
Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>