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

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>