fixed #841 (#845)
fixed #841 (#845)

* Update workspace_pool.cc

* Update workspace_pool.cc

Huyuwei/tvm,dmlc/tvm,sxjscience/tvm,Huyuwei/tvm,Laurawly/tvm-1,Huyuwei/tvm,sxjscience/tvm,tqchen/tvm,dmlc/tvm,sxjscience/tvm,dmlc/tvm,sxjscience/tvm,Laurawly/tvm-1,tqchen/tvm,Huyuwei/tvm,dmlc/tvm,tqchen/tvm,dmlc/tvm,tqchen/tvm,Laurawly/tvm-1,Huyuwei/tvm,Laurawly/tvm-1,Laurawly/tvm-1,sxjscience/tvm,Laurawly/tvm-1,dmlc/tvm,Huyuwei/tvm,dmlc/tvm,Laurawly/tvm-1,tqchen/tvm,Laurawly/tvm-1,tqchen/tvm,Huyuwei/tvm,sxjscience/tvm,dmlc/tvm,Laurawly/tvm-1,tqchen/tvm,Huyuwei/tvm,tqchen/tvm,sxjscience/tvm,Huyuwei/tvm,tqchen/tvm,Laurawly/tvm-1,tqchen/tvm,sxjscience/tvm,dmlc/tvm,sxjscience/tvm