perf data convert json: Fix trace_seq memory leak in process_sample_event()

Unlike the in-kernel trace_seq which uses a statically allocated buffer,
the userspace traceevent library's trace_seq uses a dynamically allocated
one. Therefore, every trace_seq_init() call must be paired with a
trace_seq_destroy(), otherwise it produces a memory leak.

In process_sample_event(), a trace_seq is initialized for each field when
formatting tracepoint raw_data, but the matching trace_seq_destroy() is
never called, leaking memory for every field of every sample processed.

Add the missing trace_seq_destroy() after using the trace_seq buffer to
properly free the allocated memory.

Detected with Valgrind on a perf.data file with 2,729 tracepoint samples:
  Before: definitely lost: 55,537,664 bytes in 13,559 blocks
  After:  definitely lost: 0 bytes in 0 blocks

Fixes: 9d895e4684 ("perf data: Add tracepoint fields when converting to JSON")
Signed-off-by: Tanushree Shah <tshah@linux.ibm.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

tools/perf/util/data-convert-json.c

@@ -258,6 +258,7 @@ static int process_sample_event(const struct perf_tool *tool,
 				trace_seq_init(&s);
 				tep_print_field(&s, sample->raw_data, fields[i]);
 				output_json_key_string(out, true, 3, fields[i]->name, s.buffer);
+				trace_seq_destroy(&s);
 
 				i++;
 			}