serial: liteuart: fix use-after-free and memleak on unbind

Deregister the port when unbinding the driver to prevent it from being
used after releasing the driver data and leaking memory allocated by
serial core.

Fixes: 1da81e55

 ("drivers/tty/serial: add LiteUART driver")
Cc: stable@vger.kernel.org      # 5.11
Cc: Filip Kokosinski <fkokosinski@antmicro.com>
Cc: Mateusz Holenko <mholenko@antmicro.com>
Reviewed-by: Stafford Horne <shorne@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20211117100512.5058-2-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>