tools: ifdtool: Do not write region while its size is negative

We should ignore those regions whose size is negative. These are
typically optional and unused regions (like GbE and platform data).

Change-Id: I65ad01746144604a1dc0588b617af21f2722ebbf
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>

tools/ifdtool.c

@@ -462,7 +462,7 @@ static int write_regions(char *image, int size)
 		if (ret)
 			return ret;
 		dump_region(i, frba);
-		if (region.size == 0)
+		if (region.size <= 0)
 			continue;
 		region_fd = open(region_filename(i),
 				 O_WRONLY | O_CREAT | O_TRUNC, S_IRUSR |