Add a missing break.

Patch by Tobias Güntner.

I tried to write a test, but the only difference is the Changed value that
gets returned. It can be tested with "opt -debug-pass=Executions -functionattrs,
but that doesn't seem worth it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205121 91177308-0d34-0410-b5e6-96231b3b80d8