Input: max77650-onkey - add MODULE_ALIAS()

Define a MODULE_ALIAS() in the input sub-driver for max77650 so that
the appropriate module gets loaded together with the core mfd driver.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>