libbpf: Remove unnecessary type cast

The link variable is already of type 'struct bpf_link *', casting it to
'struct bpf_link *' is redundant, drop it.
Signed-off-by: NYuntao Wang <ytcoode@gmail.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220424143420.457082-1-ytcoode@gmail.com

tools/lib/bpf/libbpf.c

@@ -11270,7 +11270,7 @@ static struct bpf_link *bpf_program__attach_btf_id(const struct bpf_program *pro
 		return libbpf_err_ptr(pfd);
 	}
 	link->fd = pfd;
-	return (struct bpf_link *)link;
+	return link;
 }
 
 struct bpf_link *bpf_program__attach_trace(const struct bpf_program *prog)