Input: cpcap-pwrbutton - do not set input parent explicitly

We are using devm_input_allocate_device() that already sets parent
of the input device, there is no need to do that again.

Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://lore.kernel.org/r/YWpiZqrfC9+GQsM4@google.com


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