perf tools: use ARRAY_SIZE

Fix the following cppcheck warnings:

./tools/perf/tests/demangle-ocaml-test.c:29:34-35: WARNING: Use ARRAY_SIZE.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.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/1615281145-2122-1-git-send-email-jiapeng.chong@linux.alibaba.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>