selftests/bpf: Clean up array_size.cocci warnings

Clean up the array_size.cocci warnings under tools/testing/selftests/bpf/:

Use `ARRAY_SIZE(arr)` instead of forms like `sizeof(arr)/sizeof(arr[0])`.

tools/testing/selftests/bpf/test_cgroup_storage.c uses ARRAY_SIZE() defined
in tools/include/linux/kernel.h (sys/sysinfo.h -> linux/kernel.h), while
others use ARRAY_SIZE() in bpf_util.h.

Signed-off-by: Guo Zhengkui <guozhengkui@vivo.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220315130143.2403-1-guozhengkui@vivo.com