perf bench numa: Avoid possible truncation when using snprintf()

Addressing this warning from gcc 7:

    CC       /tmp/build/perf/bench/numa.o
  bench/numa.c: In function '__bench_numa':
  bench/numa.c:1582:42: error: '%d' directive output may be truncated writing between 1 and 10 bytes into a region of size between 8 and 17 [-Werror=format-truncation=]
       snprintf(tname, 32, "process%d:thread%d", p, t);
                                            ^~
  bench/numa.c:1582:25: note: directive argument in the range [0, 2147483647]
       snprintf(tname, 32, "process%d:thread%d", p, t);
                           ^~~~~~~~~~~~~~~~~~~~
  In file included from /usr/include/stdio.h:939:0,
                   from bench/../util/util.h:47,
                   from bench/../builtin.h:4,
                   from bench/numa.c:11:
  /usr/include/bits/stdio2.h:64:10: note: '__builtin___snprintf_chk' output between 17 and 35 bytes into a destination of size 32
     return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          __bos (__s), __fmt, __va_arg_pack ());
          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  cc1: all warnings being treated as errors

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Petr Holasek <pholasek@redhat.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-twa37vsfqcie5gwpqwnjuuz9@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/bench/numa.c

@@ -1573,13 +1573,13 @@ static int __bench_numa(const char *name)
 		"GB/sec,", "total-speed",	"GB/sec total speed");
 
 	if (g->p.show_details >= 2) {
-		char tname[32];
+		char tname[14 + 2 * 10 + 1];
 		struct thread_data *td;
 		for (p = 0; p < g->p.nr_proc; p++) {
 			for (t = 0; t < g->p.nr_threads; t++) {
-				memset(tname, 0, 32);
+				memset(tname, 0, sizeof(tname));
 				td = g->threads + p*g->p.nr_threads + t;
-				snprintf(tname, 32, "process%d:thread%d", p, t);
+				snprintf(tname, sizeof(tname), "process%d:thread%d", p, t);
 				print_res(tname, td->speed_gbs,
 					"GB/sec",	"thread-speed", "GB/sec/thread speed");
 				print_res(tname, td->system_time_ns / NSEC_PER_SEC,