gpio: tps65218: remove unneeded callbacks

GPIO core can handle output-only chips that don't implement the get()
and direction_input() callbacks. There's no need to provide dummy
implementation of the latter in the driver so drop it.

Link: https://lore.kernel.org/r/20250702-gpiochip-set-rv-gpio-round3-v1-9-0d23be74f71d@linaro.org


Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>