perf tools: Fix perf_evsel::exclude_GH handling

perf tools: Fix perf_evsel::exclude_GH handling

Let the perf_evsel::exclude_GH only prevent the reset of exclude_host
and exclude_guest attributes in case they were already set.

We cannot reset their values to 0, because they might have other
defaults set by event_attr_init.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1359971803-2343-2-git-send-email-jolsa@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>