UefiCpuPkg/PiSmmCpuDxeSmm: Simplify RunningApCount decrement

To decrease the count of RunningApCount, InterlockedDecrement is
enough to achieve that.

This patch is to simplify RunningApCount decrement.

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Zeng Star <star.zeng@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Signed-off-by: Jiaxin Wu <jiaxin.wu@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>

UefiCpuPkg/PiSmmCpuDxeSmm/MpService.c

@@ -1452,7 +1452,7 @@ InternalSmmStartupAllAPs (
       // Decrease the count to mark this processor(AP or BSP) as finished.
       //
       if (ProcToken != NULL) {
-        WaitForSemaphore (&ProcToken->RunningApCount);
+        InterlockedDecrement (&ProcToken->RunningApCount);
       }
     }
   }