tools: Avoid leaving extra data at the end of copied files

The copyfile() implementation has strange behaviour if the destination
file already exists. Update it to ensure that any existing data in the
destination file is dropped.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/fit_common.c

@@ -134,7 +134,7 @@ int copyfile(const char *src, const char *dst)
 		goto out;
 	}
 
-	fd_dst = open(dst, O_WRONLY | O_CREAT, 0666);
+	fd_dst = open(dst, O_WRONLY | O_CREAT | O_TRUNC, 0666);
 	if (fd_dst < 0) {
 		printf("Can't open file %s (%s)\n", dst, strerror(errno));
 		goto out;