libbpf: Fix array_size.cocci warning

Fix the following coccicheck warning:
tools/lib/bpf/bpf.c:114:31-32: WARNING: Use ARRAY_SIZE
tools/lib/bpf/xsk.c:484:34-35: WARNING: Use ARRAY_SIZE
tools/lib/bpf/xsk.c:485:35-36: WARNING: Use ARRAY_SIZE

It has been tested with gcc (Debian 8.3.0-6) 8.3.0 on x86_64.

Signed-off-by: Guo Zhengkui <guozhengkui@vivo.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220306023426.19324-1-guozhengkui@vivo.com

src/bpf.c

@@ -29,6 +29,7 @@
 #include <errno.h>
 #include <linux/bpf.h>
 #include <linux/filter.h>
+#include <linux/kernel.h>
 #include <limits.h>
 #include <sys/resource.h>
 #include "bpf.h"
@@ -111,7 +112,7 @@ int probe_memcg_account(void)
 		BPF_EMIT_CALL(BPF_FUNC_ktime_get_coarse_ns),
 		BPF_EXIT_INSN(),
 	};
-	size_t insn_cnt = sizeof(insns) / sizeof(insns[0]);
+	size_t insn_cnt = ARRAY_SIZE(insns);
 	union bpf_attr attr;
 	int prog_fd;