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

lib/Target/PowerPC/InstPrinter/PPCInstPrinter.cpp

@@ -90,7 +90,6 @@ void PPCInstPrinter::printPredicateOperand(const MCInst *MI, unsigned OpNo,
 
   if (StringRef(Modifier) == "cc") {
     switch ((PPC::Predicate)Code) {
-    default: llvm_unreachable("Bad predicate!");
     case PPC::PRED_LT: O << "lt"; return;
     case PPC::PRED_LE: O << "le"; return;
     case PPC::PRED_EQ: O << "eq"; return;