BaseTools/GenFv: Fix parameter format mismatch in scanf functions

BaseTools/GenFv: Fix parameter format mismatch in scanf functions

According to MSDN https://msdn.microsoft.com/en-us/library/6ttkkkhh.aspx &
https://msdn.microsoft.com/en-us/library/xdb9w69d.aspx

Format specification '%llx' for scanf expects type 'long long *', modify
the type of the relating variable to 'long long' 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>