IntelFsp2Pkg/Tools: Fix a typo issue
    
    Error message:
    raise Exception ("'%s' is not a valid directory!" % FvDir)
    NameError: name 'FvDir' is not defined
    
    FvDir should be fvDir.
    
    Cc: Chasel Chiu <chasel.chiu@intel.com>
    Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
    Cc: Star Zeng <star.zeng@intel.com>
    Signed-off-by: Yunhua Feng <fengyunhua@byosoft.com.cn>
    Reviewed-by: Chasel Chiu <chasel.chiu@intel.com>
    Reviewed-by: Nate DeSimone <nathaniel.l.desimone@intel.com>