sandbox: drop unused return

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Acked-by: Simon Glass <sjg@chromium.org>

arch/sandbox/cpu/start.c

@@ -28,6 +28,4 @@ int main(int argc, char *argv[])
 	 * never return.
 	 */
 	board_init_f(0);
-
-	return 0;
 }