libbpf: Fix error message in attach_kprobe_multi

We just failed to retrieve pattern, so we need to print spec instead.

Fixes: ddc6b049 ("libbpf: Add bpf_program__attach_kprobe_multi_opts function")
Reported-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240502075541.1425761-2-jolsa@kernel.org

tools/lib/bpf/libbpf.c

@@ -11579,7 +11579,7 @@ static int attach_kprobe_multi(const struct bpf_program *prog, long cookie, stru
 
 	n = sscanf(spec, "%m[a-zA-Z0-9_.*?]", &pattern);
 	if (n < 1) {
-		pr_warn("kprobe multi pattern is invalid: %s\n", pattern);
+		pr_warn("kprobe multi pattern is invalid: %s\n", spec);
 		return -EINVAL;
 	}