libperf cpumap: Take into advantage it is sorted to optimize perf_cpu_map__max()

From commit 7074674e73 ("perf cpumap: Maintain cpumaps ordered and
without dups"), perf_cpu_map elements are sorted in ascending order.

This patch improves the perf_cpu_map__max function by returning the last
element.

Committer notes:

Do it as a ternary to keep it in just one return line, add a comment
explaining it is sorted and what functions does it.

Signed-off-by: Riccardo Mancini <rickyman7@gmail.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/fb79f02e7b86ea8044d563adb1e9890c906f982f.1629490974.git.rickyman7@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/perf/cpumap.c

@@ -282,14 +282,8 @@ int perf_cpu_map__idx(struct perf_cpu_map *cpus, int cpu)
 
 int perf_cpu_map__max(struct perf_cpu_map *map)
 {
-	int i, max = -1;
-
-	for (i = 0; i < map->nr; i++) {
-		if (map->map[i] > max)
-			max = map->map[i];
-	}
-
-	return max;
+	// cpu_map__trim_new() qsort()s it, cpu_map__default_new() sorts it as well.
+	return map->nr > 0 ? map->map[map->nr - 1] : -1;
 }
 
 /*