powerpc: fix -Wimplicit-fallthrough

The "fallthrough" pseudo-keyword was added as a portable way to denote
intentional fallthrough. Clang will still warn on cases where there is a
fallthrough to an immediate break. Add explicit breaks for those cases.

Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://github.com/ClangBuiltLinux/linux/issues/236
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

arch/powerpc/kernel/prom_init.c

@@ -355,6 +355,7 @@ static int __init prom_strtobool(const char *s, bool *res)
 		default:
 			break;
 		}
+		break;
 	default:
 		break;
 	}

arch/powerpc/kernel/uprobes.c

@@ -141,6 +141,7 @@ int arch_uprobe_exception_notify(struct notifier_block *self,
 	case DIE_SSTEP:
 		if (uprobe_post_sstep_notifier(regs))
 			return NOTIFY_STOP;
+		break;
 	default:
 		break;
 	}

arch/powerpc/perf/imc-pmu.c

@@ -1500,6 +1500,7 @@ static int update_pmu_ops(struct imc_pmu *pmu)
 		pmu->pmu.stop = trace_imc_event_stop;
 		pmu->pmu.read = trace_imc_event_read;
 		pmu->attr_groups[IMC_FORMAT_ATTR] = &trace_imc_format_group;
+		break;
 	default:
 		break;
 	}