Revert r183854 (PPC: Fix switch warnings from r183841)

Now that the PRED_BAD has been removed, this is failing the Clang
-Werror build due to -Wcovered-switch-default.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183863 91177308-0d34-0410-b5e6-96231b3b80d8