UefiCpuPkg/MpInitLib: Set initialize value of TimerPeriod

This fix is to pass VS2010/VS2012 build.

Cc: Feng Tian <feng.tian@intel.com>
Cc: Dandan Bi <dandan.bi@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jeff Fan <jeff.fan@intel.com>
Reviewed-by: Dandan Bi <dandan.bi@intel.com>

UefiCpuPkg/Library/MpInitLib/DxeMpLib.c

@@ -651,6 +651,7 @@ MpInitLibSwitchBSP (
   EFI_TIMER_ARCH_PROTOCOL      *Timer;
   UINT64                       TimerPeriod;
 
+  TimerPeriod = 0;
   //
   // Locate Timer Arch Protocol
   //