bpf: Add missing btf_put to register_btf_id_dtor_kfuncs

We take the BTF reference before we register dtors and we need
to put it back when it's done.

We probably won't se a problem with kernel BTF, but module BTF
would stay loaded (because of the extra ref) even when its module
is removed.

Cc: Kumar Kartikeya Dwivedi <[email protected]>
Fixes: 5ce937d ("bpf: Populate pairs of btf_id and destructor kfunc in btf")
Acked-by: Kumar Kartikeya Dwivedi <[email protected]>
Signed-off-by: Jiri Olsa <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: olsajiri

kernel/bpf/btf.c

@@ -7782,9 +7782,9 @@ int register_btf_id_dtor_kfuncs(const struct btf_id_dtor_kfunc *dtors, u32 add_c
 
 	sort(tab->dtors, tab->cnt, sizeof(tab->dtors[0]), btf_id_cmp_func, NULL);
 
-	return 0;
 end:
-	btf_free_dtor_kfunc_tab(btf);
+	if (ret)
+		btf_free_dtor_kfunc_tab(btf);
 	btf_put(btf);
 	return ret;
 }