Fixed build warning with -DLIBOMP_USE_HWLOC=1

Made type of depth of hwloc object to correapond with
change from unsigned in hwloc 1,x to int in hwloc 2.x.
This eliminates the warning on signed-unsigned comparison.

Differential Revision: https://reviews.llvm.org/D62332


git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@362401 91177308-0d34-0410-b5e6-96231b3b80d8