Panic when no command line processing can be performed

Normally board_run_command() will handle command processed. But if for some
reason it returns then we should panic to avoid further processing.

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

common/main.c

@@ -72,4 +72,5 @@ void main_loop(void)
 	autoboot_command(s);
 
 	cli_loop();
+	panic("No CLI available");
 }