tools: kwboot: Fix checking image header version

Function image_version() returns unsigned value, so it can never be
negative. Explicitly check for two supported image versions: v0 and v1.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Stefan Roese <sr@denx.de>

tools/kwboot.c

@@ -634,7 +634,7 @@ kwboot_img_patch_hdr(void *img, size_t size)
 	}
 
 	image_ver = image_version(img);
-	if (image_ver < 0) {
+	if (image_ver != 0 && image_ver != 1) {
 		fprintf(stderr, "Invalid image header version\n");
 		errno = EINVAL;
 		goto out;