IntelFsp2WrapperPkg: Add variable initialization

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4595

Fix build error when remove "-Wno-sometimes-uninitialized" option,
Add variable "FspMultiPhaseApiOffset" initialization.

Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Chasel Chiu <chasel.chiu@intel.com>
Cc: Duggapu Chinni B <chinni.b.duggapu@intel.com>
Cc: Ted Kuo <ted.kuo@intel.com>
Cc: Susovan Mohapatra <susovan.mohapatra@intel.com>
Cc: James Lu <james.lu@intel.com>
Reviewed-by: Ashraf Ali S <ashraf.ali.s@intel.com>
Reviewed-by: Chen Gang C <gang.c.chen@intel.com>
Reviewed-by: Gua Guo <gua.guo@intel.com>
Signed-off-by: Jason Hsu <jasonx.hsu@intel.com>

Author: yunhsiax

IntelFsp2WrapperPkg/Library/FspWrapperMultiPhaseProcessLib/PeiFspWrapperMultiPhaseProcessLib.c

@@ -80,6 +80,7 @@ CallFspMultiPhaseEntry (
   BOOLEAN                 IsVariableServiceRequest;
   FSP_MULTI_PHASE_PARAMS  *FspMultiPhaseParamsPtr;
 
+  FspMultiPhaseApiOffset   = 0;
   FspMultiPhaseParamsPtr   = (FSP_MULTI_PHASE_PARAMS *)FspMultiPhaseParams;
   IsVariableServiceRequest = FALSE;
   if ((FspMultiPhaseParamsPtr->MultiPhaseAction == EnumMultiPhaseGetVariableRequestInfo) ||