serial_find_console_or_panic() may left cur_serial_dev unassigned if REQUIRE_SERIAL_CONSOLE is not set. Setting GD_FLG_SERIAL_READY in this situation confuses serial console code. It tries to use unassigned driver instead of debug port and stops printing. So check cur_serial_dev before setting GD_FLG_SERIAL_READY to allow console to keep printing via debug port. Signed-off-by: Maxim Kochetkov <fido_max@inbox.ru>