tools/bpf: silence a libbpf unnecessary warning

Commit 96408c43 ("tools/bpf: implement libbpf
btf__get_map_kv_tids() API function") refactored
function bpf_map_find_btf_info() and moved bulk of
implementation into btf.c as btf__get_map_kv_tids().
This change introduced a bug such that test_btf will
print out the following warning although the test passed:
  BTF libbpf test[2] (test_btf_nokv.o): libbpf: map:btf_map
      container_name:____btf_map_btf_map cannot be found
      in BTF. Missing BPF_ANNOTATE_KV_PAIR?

Previously, the error message is guarded with pr_debug().
Commit 96408c43 changed it to pr_warning() and
hence caused the warning.

Restoring to pr_debug() for the message fixed the issue.

Fixes: 96408c43 ("tools/bpf: implement libbpf btf__get_map_kv_tids() API function")
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/lib/bpf/btf.c

@@ -531,8 +531,8 @@ int btf__get_map_kv_tids(const struct btf *btf, const char *map_name,
 
 	container_id = btf__find_by_name(btf, container_name);
 	if (container_id < 0) {
-		pr_warning("map:%s container_name:%s cannot be found in BTF. Missing BPF_ANNOTATE_KV_PAIR?\n",
-			   map_name, container_name);
+		pr_debug("map:%s container_name:%s cannot be found in BTF. Missing BPF_ANNOTATE_KV_PAIR?\n",
+			 map_name, container_name);
 		return container_id;
 	}