Input: arizona-haptic - don't assign input_dev parent

We shouldn't assign the parent device of the input_dev to be the
parent MFD device, because this will be used for devres which causes
input_unregister_device to run after the haptics device has been
removed, since it is itself a child of the MFD device. The default
of using the haptics device itself as the parent is correct.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>