[llvm-profdata] Fix unhandled enumeration values warning

Fix this:

llvm/tools/llvm-profdata/llvm-profdata.cpp:78:15: warning: 12 enumeration values not handled in switch: 'success', 'eof', 'unrecognized_format'... [-Wswitch]
      switch (instrError) {
                    ^

llvm-svn: 253413

tools/llvm-profdata/llvm-profdata.cpp

@@ -82,6 +82,8 @@ static void handleMergeWriterError(std::error_code &Error,
         Hint = "Make sure that all profile data to be merged is generated " \
                "from the same binary.";
         break;
+      default:
+        break;
       }
     }