Debug Info: remove form from function addDIEEntry.

The form must be a reference form in addDIEEntry. Which reference form to
use will be decided by the callee.

No functionality change.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192517 91177308-0d34-0410-b5e6-96231b3b80d8