OvmfPkg/PciHostBridgeLib: clear PCI aperture vars for (re)init

Use ZeroMem() to initialize (or re-initialize) all fields in temporary
PCI_ROOT_BRIDGE_APERTURE variables to zero. This is not mandatory but
is helpful for future extension: when we add new fields to
PCI_ROOT_BRIDGE_APERTURE and the default value of these fields can
safely be zero, this code will not suffer from an additional
change.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Heyi Guo <heyi.guo@linaro.org>
Signed-off-by: Yi Li <phoenix.liyi@huawei.com>
Reviewed-by: Ni Ruiyu <ruiyu.ni@intel.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

OvmfPkg/Library/PciHostBridgeLib/PciHostBridgeLib.c

@@ -221,6 +221,10 @@ PciHostBridgeGetRootBridges (
     return ScanForRootBridges (Count);
   }
 
+  ZeroMem (&Io, sizeof (Io));
+  ZeroMem (&Mem, sizeof (Mem));
+  ZeroMem (&MemAbove4G, sizeof (MemAbove4G));
+
   Attributes = EFI_PCI_ATTRIBUTE_IDE_PRIMARY_IO |
     EFI_PCI_ATTRIBUTE_IDE_SECONDARY_IO |
     EFI_PCI_ATTRIBUTE_ISA_IO_16 |