DebugInfo: Use DebugNodeRef in MDImportedEntity::getEntity()

A quick cleanup to sue `DebugNodeRef` instead of `Metadata*` for
`MDImportedEntity::getEntity()`.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234288 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed