Input: make input_report_slot_state() return boolean

Let's make input_report_slot_state() return boolean representing whether
the contact is active or not. This will allow writing code like:

	if (input_mt_report_slot_state(input, obj->mt_tool,
					obj->type != RMI_2D_OBJECT_NONE) {

		input_event(sensor->input, EV_ABS, ABS_MT_POSITION_X, obj->x);
		input_event(sensor->input, EV_ABS, ABS_MT_POSITION_Y, obj->y);
		...
	}

instead of:

	input_mt_report_slot_state(input, obj->mt_tool,
				   obj->type != RMI_2D_OBJECT_NONE);
	if (obj->type != RMI_2D_OBJECT_NONE) {
		input_event(sensor->input, EV_ABS, ABS_MT_POSITION_X, obj->x);
		input_event(sensor->input, EV_ABS, ABS_MT_POSITION_Y, obj->y);
		...
	}

Reviewed-by: Henrik Rydberg <rydberg@bitmath.org>
Acked-by: Benjamin Tissoires <benjamin.tissoires@redaht.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>