Return *Col instead c *Col
Return *Col instead c *Col

Make code more readable

Signed-off-by: ZhiFeng Hu <abb672b28ca55a560b8a96028ef4fd2c71d0292b@gmail.com>

ueizhou/tidb,andelf/tidb,c4pt0r/tidb,silenceper/tidb,qhsong/tidb,EvilMcJerkface/tidb,cosmtrek/tidb,c4pt0r/tidb,XuHuaiyu/tidb,myrice/tidb,netroby/tidb,Nify/tidb,ngaut/tidb,spongedu/tidb,tiancaiamao/tidb,kyle-wang/tidb,yangwenmai/tidb,ming-relax/tidb,liyu4/tidb,astaxie/tidb,kyle-wang/tidb,EvilMcJerkface/tidb,ngaut/tidb,pingcap/tidb,pingcap/tidb,pingcap/tidb,spongedu/tidb,pingcap/tidb,ueizhou/tidb,Cofyc/tidb,c4pt0r/tidb,yuanwhy/tidb,qiuyesuifeng/tidb,kyle-wang/tidb,gaocegege/tidb,anywhy/tidb,netroby/tidb,yangwenmai/tidb,zs634134578/tidb,myrice/tidb,wusphinx/tidb,gaocegege/tidb,simon-xia/tidb,ming-relax/tidb,8cbx/tidb,qiuyesuifeng/tidb,kyle-wang/tidb,silentred/tidb,mccxj/tidb,yuanwhy/tidb,JinheLin/tidb,liyu4/tidb,ngaut/tidb,tiancaiamao/tidb,silenceper/tidb,anywhy/tidb,mccxj/tidb,Nify/tidb,8cbx/tidb,CodeRushing/tidb,c4pt0r/tidb,coocood/tidb,silentred/tidb,simon-xia/tidb,ngaut/tidb,wusphinx/tidb,ngaut/tidb,CodeRushing/tidb,JinheLin/tidb,pingcap/tidb,zimulala/tidb,coocood/tidb,Cofyc/tidb,louishust/tidb,astaxie/tidb,zimulala/tidb,andelf/tidb,c4pt0r/tidb,qhsong/tidb,zs634134578/tidb,cosmtrek/tidb,XuHuaiyu/tidb,louishust/tidb,c4pt0r/tidb,ngaut/tidb,pingcap/tidb,kyle-wang/tidb,kyle-wang/tidb