Input: ams_delta_serio - fix wrong kfree in ams_delta_serio_exit

serio_unregister_port() will call put_device() to free the memory.
Thus remove kfree(ams_delta_serio) after
serio_unregister_port(ams_delta_serio).

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>