tools lib traceevent: Fix error path on pevent_parse_event

If __pevent_parse_format() succeeded but add_event() failed, 'ret' didn't
have a proper error code.  Set it to PEVENT_ERRNO__MEM_ALLOC_FAILED.

In addition, at that point 'event' also has fields and format
information and they all need to be freed.  Call pevent_free_format() to
handle it.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1348575919-4954-1-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>