IntelFsp2Pkg/SplitFspBin.py: Coverity scan flags issues.
    
    REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1706
    
    Issues were:
    1. copy_paste_error: PeOptHdr vs PePlusOptHdr.
    2. invalid_operation: Invalid operation on
    null-like value "roffset".
    3. invalid_operation: Invalid operation on
    null-like value "rsize".
    
    Fixed them by initializing roffset and rsize as PE32
    image type and overriding them when PE32+ header found.
    
    Test:
    Compared script output before and after this patch and
    the result is identical.
    
    Cc: Maurice Ma <maurice.ma@intel.com>
    Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
    Cc: Star Zeng <star.zeng@intel.com>
    Signed-off-by: Chasel Chiu <chasel.chiu@intel.com>
    Reviewed-by: Star Zeng <star.zeng@intel.com>
    Reviewed-by: Nate DeSimone <nathaniel.l.desimone@intel.com>