perf record: Fix typo in pid_synthesize_comm_event

We were using 'fd' locally, but there was a global 'fd' too, so
when converting from open to fopen the test made against fd
should be made against 'fp', but since we have that global
it didnt get discovered ...

Reported-by: Ulrich Drepper <drepper@redhat.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20090814182632.GF3490@ghostprotocols.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>