Input: libps2 - rework handling of command response

It is not entirely correct that libps2 sets PS2_FLAG_CMD1 after
the device acknowledges each byte sent to the device by the host.
Rework the code so that PS2_FLAG_CMD1 and PS2_FLAG_CMD are set only once,
at the beginning of PS/2 command execution.

Reviewed-by: Raul E Rangel <rrangel@chromium.org>
Link: https://lore.kernel.org/r/20230511185252.386941-4-dmitry.torokhov@gmail.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>