Fix implicit fall through switch cases.

Bug: 116020901

Test: Builds with -Werror=implicit-fallthrough.
Change-Id: I401f37585dae6cbf8995389a8a189abc2e102987
diff --git a/libunwindstack/DwarfSection.cpp b/libunwindstack/DwarfSection.cpp
index 6061f61..57a780e 100644
--- a/libunwindstack/DwarfSection.cpp
+++ b/libunwindstack/DwarfSection.cpp
@@ -461,6 +461,7 @@
       if (reg == eval_info->cie->return_address_register) {
         eval_info->return_address_undefined = true;
       }
+      break;
     default:
       break;
   }