Fix coverity defects: CID 147571, 147574
CID 147571: Unintentional integer overflow (OVERFLOW_BEFORE_WIDEN)
CID 147574: Unintentional integer overflow (OVERFLOW_BEFORE_WIDEN)
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: luozhengzheng <luo.zhengzheng@zte.com.cn>
Closes #5268