mkimage: Require a data file when auto-fit is used

When auto-fit is used, it is not valid to create a FIT without an image
file. Add a check for this to avoid a very confusing error message later
("Can't open (null): Bad address").

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>

tools/mkimage.c

@@ -276,6 +276,8 @@ static void process_args(int argc, char **argv)
 		/* For auto_its, datafile is always 'auto' */
 		if (!params.auto_its)
 			params.datafile = datafile;
+		else if (!params.datafile)
+			usage("Missing data file for auto-FIT (use -d)");
 	} else if (type != IH_TYPE_INVALID) {
 		params.type = type;
 	}