BaseTools/GenVtf: Fix parameter format mismatch in scanf functions

According to MSDN https://msdn.microsoft.com/en-us/library/6ttkkkhh.aspx

Format specification '%x' for scanf expects type 'int *', modify the type
of the relating variable to 'int' to keep them matched.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

BaseTools/Source/C/GenVtf/GenVtf.c

@@ -112,8 +112,8 @@ Returns:
 --*/
 {
   CHAR8  TemStr[5] = "0000";
-  unsigned Major;
-  unsigned Minor;
+  int    Major;
+  int    Minor;
   UINTN Length;
 
   Major = 0;