[CodeGen] Rename DEBUG_TYPE to match passnames

Rename missing DEBUG_TYPE "machine-scheduler" from backend files, which were
absent from https://reviews.llvm.org/rL303921.

Differential revision: https://reviews.llvm.org/D35231

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@307719 91177308-0d34-0410-b5e6-96231b3b80d8
11 files changed