bpftool: Fix errno variable usage

The test meant to use the saved value of errno. Given the current code, it
makes no practical difference however.

Fixes: bf598a8f ("bpftool: Improve handling of ENOENT on map dumps")
Signed-off-by: Benjamin Poirier <bpoirier@suse.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/bpf/bpftool/map.c

@@ -724,7 +724,7 @@ static int dump_map_elem(int fd, void *key, void *value,
 	} else {
 		const char *msg = NULL;
 
-		if (errno == ENOENT)
+		if (lookup_errno == ENOENT)
 			msg = "<no entry>";
 		else if (lookup_errno == ENOSPC &&
 			 map_info->type == BPF_MAP_TYPE_REUSEPORT_SOCKARRAY)