Input: twl4030-pwrbutton - drop redundant pwr->dev.parent assignment

devm_input_allocate_device() already initializes pwr->dev.parent to the
supplied parent device, so the explicit assignment in
twl4030_pwrbutton_probe() is redundant. Remove it.

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