bpf/tests: Use struct_size()

Use struct_size() instead of hand writing it. This is less verbose and
more informative.
Signed-off-by: Su Hui <suhui@nfschina.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20230531043251.989312-1-suhui@nfschina.com

lib/test_bpf.c

@@ -15056,8 +15056,7 @@ static __init int prepare_tail_call_tests(struct bpf_array **pprogs)
 	int which, err;
 
 	/* Allocate the table of programs to be used for tall calls */
-	progs = kzalloc(sizeof(*progs) + (ntests + 1) * sizeof(progs->ptrs[0]),
-			GFP_KERNEL);
+	progs = kzalloc(struct_size(progs, ptrs, ntests + 1), GFP_KERNEL);
 	if (!progs)
 		goto out_nomem;