speakup: Make dectlk flush timeout configurable

In case the serial port or cable got faulty, we may not be getting
acknowledgements any more. The driver then currently waits for 4s to
avoid jamming the device. This makes this delay configurable.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Link: https://lore.kernel.org/r/20210128180116.1848120-3-samuel.thibault@ens-lyon.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>