bpftool: Fix build warnings with -Wtype-limits

Quentin reported build warnings when building bpftool :

    link.c: In function ‘perf_config_hw_cache_str’:
    link.c:86:18: warning: comparison of unsigned expression in ‘>= 0’ is always true [-Wtype-limits]
       86 |         if ((id) >= 0 && (id) < ARRAY_SIZE(array))      \
          |                  ^~
    link.c:320:20: note: in expansion of macro ‘perf_event_name’
      320 |         hw_cache = perf_event_name(evsel__hw_cache, config & 0xff);
          |                    ^~~~~~~~~~~~~~~
    [... more of the same for the other calls to perf_event_name ...]

He also pointed out the reason and the solution:

  We're always passing unsigned, so it should be safe to drop the check on
  (id) >= 0.

Fixes: 62b57e3d ("bpftool: Add perf event names")
Reported-by: Quentin Monnet <quentin@isovalent.com>
Suggested-by: Quentin Monnet <quentin@isovalent.com>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Quentin Monnet <quentin@isovalent.com>
Closes: https://lore.kernel.org/bpf/a35d9a2d-54a0-49ec-9ed1-8fcf1369d3cc@isovalent.com
Link: https://lore.kernel.org/bpf/20230830030325.3786-1-laoar.shao@gmail.com

tools/bpf/bpftool/link.c

@@ -83,7 +83,7 @@ const char *evsel__hw_cache_result[PERF_COUNT_HW_CACHE_RESULT_MAX] = {
 #define perf_event_name(array, id) ({			\
 	const char *event_str = NULL;			\
 							\
-	if ((id) >= 0 && (id) < ARRAY_SIZE(array))	\
+	if ((id) < ARRAY_SIZE(array))			\
 		event_str = array[id];			\
 	event_str;					\
 })