DWARF reader: fix case statement fall-through warning

This change eliminates a compiler warning. There is no change in
behaviour as the following cases immediately break.

	src/abg-dwarf-reader.cc (die_pretty_print_type): Add a missing
	break statement at the end of the DW_TAG_string_type case.

Change-Id: If6e955ec87c9af2917c194978eee5fb9fdc0ea38
Signed-off-by: Giuliano Procida <gprocida@google.com>
diff --git a/src/abg-dwarf-reader.cc b/src/abg-dwarf-reader.cc
index 3f71694..d8e02a0 100644
--- a/src/abg-dwarf-reader.cc
+++ b/src/abg-dwarf-reader.cc
@@ -9734,6 +9734,7 @@
       // this to be a lot of hassle for no great return.  Until proven
       // otherwise, of course.
       repr = "string type";
+      break;
 
     case DW_TAG_unspecified_type:
     case DW_TAG_ptr_to_member_type: