perf header: Use evlist->nr_entries on write_event_desc()

Number of events (evsels) in a evlist is kept on nr_entries field
so that we don't need to recalculate it.
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1346821373-31621-2-git-send-email-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/header.c

@@ -610,11 +610,10 @@ static int write_event_desc(int fd, struct perf_header *h __used,
 			    struct perf_evlist *evlist)
 {
 	struct perf_evsel *evsel;
-	u32 nre = 0, nri, sz;
+	u32 nre, nri, sz;
 	int ret;
 
-	list_for_each_entry(evsel, &evlist->entries, node)
-		nre++;
+	nre = evlist->nr_entries;
 
 	/*
 	 * write number of events