MdeModulePkg: Fix PciBus hang issue

MdeModulePkg: Fix PciBus hang issue

LocatePciExpressCapabilityRegBlock () doesn't check the return status of Pci.Read().
Certain platform's PciRootBridge.Pci.Read() doesn't support PCIE access causing the CapabilityEntry not updated.
If the uninitialized CapabilityEntry equals to a big enough initial value, the while-loop will never end.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Maurice Ma <maurice.ma@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17513 6f19259b-4bc3-4df7-8a09-765794883524