tools: mkimage: don't print error message "Success" in case of failure

In case there's no struct image_type_params::set_header callback, no
"errno" will be set. Don't fail with an error message, followed by
"Success". Remove the printing of the human readable "errno" value.

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/mkimage.c b/tools/mkimage.c
index 0b5ee5d..8306861 100644
--- a/tools/mkimage.c
+++ b/tools/mkimage.c
@@ -765,8 +765,8 @@
 	if (tparams->set_header)
 		tparams->set_header (ptr, &sbuf, ifd, &params);
 	else {
-		fprintf (stderr, "%s: Can't set header for %s: %s\n",
-			params.cmdname, tparams->name, strerror(errno));
+		fprintf (stderr, "%s: Can't set header for %s\n",
+			params.cmdname, tparams->name);
 		exit (EXIT_FAILURE);
 	}