libbpf: Fix map index used in error message

The error message emitted by bpf_object__init_user_btf_maps() was using the
wrong section ID.

Signed-off-by: Toke Høiland-Jørgensen <[e-mail]>
Signed-off-by: Daniel Borkmann <[e-mail]>
Acked-by: Yonghong Song <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/lib/bpf/libbpf.c

···
 		data = elf_getdata(scn, NULL);
 	if (!scn || !data) {
 		pr_warn("failed to get Elf_Data from map section %d (%s)\n",
-			obj->efile.maps_shndx, MAPS_ELF_SEC);
+			obj->efile.btf_maps_shndx, MAPS_ELF_SEC);
 		return -EINVAL;
 	}