Fix checks on schedule struct

This change fixes an error in comparing the existing schedule on the team to
the new schedule, in the chunk field. Also added additional checks and used
KMP_CHECK_UPDATE where appropriate.

Patch by Terry Wilmarth.

Differential Revision: http://reviews.llvm.org/D21897


git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@274371 91177308-0d34-0410-b5e6-96231b3b80d8