MdeModulePkg: Skip invalid bus number scanning in PciBusDxe driver

MdeModulePkg: Skip invalid bus number scanning in PciBusDxe driver

When PcdPciDisableBusEnumeration is enabled, the PciBus driver
might get into a dead loop if the secondary bus register on PCI
bridge is not programmed or programmed improperly. Adding this
check to avoid any potential dead loop caused by this.

Cc: Feng Tian <feng.tian@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Maurice Ma <maurice.ma@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Lee Leahy <Leroy.p.leahy@intel.com>