pie: Warn about unknown for log-simple format

Reported-by: Artem Kuzmitskiy <artem.kuzmitskiy@gmail.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

pie/log-simple.c

@@ -243,6 +243,10 @@ void sbuf_printf(struct simple_buf *b, const char *format, va_list args)
 			else
 				print_hex(va_arg(args, unsigned int), b);
 			break;
+		default:
+			print_string("UNKNOWN FORMAT ", b);
+			sbuf_putc(b, *s);
+			break;
 		}
 		s++;
 	}