OvmfPkg/PlatformPei: suppress wrong VS2008 warning (use of uninited local)

OvmfPkg/PlatformPei: suppress wrong VS2008 warning (use of uninited local)

VS2008 seems to think that the "PciExBarBase" variable (introduced in
commit 7b8fe63561b4) can be evaluated for the
AddReservedMemoryBaseSizeHob() function call with its value being
uninitialized / indeterminate. This is not the case (see
"mHostBridgeDevId"); suppress the warning.

Reported-by: David Woodhouse <dwmw2@infradead.org>
Ref: http://thread.gmane.org/gmane.comp.bios.edk2.devel/8871/focus=9431
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: David Woodhouse <David.Woodhouse@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>