[PAuthLR] Fix unannoted fallthrough

There was a missing break, which led to an unannotated fallthrough
when merging llvm#112171. This has caused sanitizer builds to fail.

This adds the missing break in the switch statement to ensure that
the fallthrough does not occur.

Author: Stylie777

llvm/lib/CodeGen/MachineOperand.cpp

@@ -772,6 +772,7 @@ static void printCFI(raw_ostream &OS, const MCCFIInstruction &CFI,
     OS << "negate_ra_sign_state_with_pc ";
     if (MCSymbol *Label = CFI.getLabel())
       MachineOperand::printSymbol(OS, *Label);
+    break;
   default:
     // TODO: Print the other CFI Operations.
     OS << "<unserializable cfi directive>";