sim: ppc: phb: add missing break to address decoder

I don't know what this emulation does exactly, but it missing a break
statement seems kind of obvious based on the 32-bit case above it.
diff --git a/sim/ppc/hw_phb.c b/sim/ppc/hw_phb.c
index ec1119e..06eb29f 100644
--- a/sim/ppc/hw_phb.c
+++ b/sim/ppc/hw_phb.c
@@ -652,6 +652,7 @@
 	     && val != 0x10 && val != 0x18 && val != 0x20)
       device_error(me, "Register number (0x%lx) invalid in 64bit PCI address %s",
 		   val, unit);
+    break;
   case ss_config_code:
     device_error(me, "internal error");
   }