Using for_each_set_bit() to simplify the code.

spatch with a semantic match is used to found this.
(http://coccinelle.lip6.fr/)
Signed-off-by: NWei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: NHaojian Zhuang <haojian.zhuang@gmail.com>