perf tools: Free 'printk' string in parse_ftrace_printk()

parse_ftrace_printk() tokenizes and parses a line, calling strdup() each
iteration.  Add code to free this temporary format string duplicate.

Fixes the following coverity complaints:

  Error: RESOURCE_LEAK (CWE-772):
  tools/perf/util/trace-event-parse.c:158: overwrite_var: Overwriting
  "printk" in "printk = strdup(fmt + 1)" leaks the storage that "printk"
  points to.

  tools/perf/util/trace-event-parse.c:162: leaked_storage: Variable
  "printk" going out of scope leaks the storage it points to.

Signed-off-by: Sanskriti Sharma <sansharm@redhat.com>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Cc: Joe Lawrence <joe.lawrence@redhat.com>
Link: http://lkml.kernel.org/r/1538490554-8161-4-git-send-email-sansharm@redhat.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>