Input: stmpe-keypad - drop redundant input->dev.parent assignment

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

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