mfd: max77693: Add haptic of_compatible in mfd_cell

This patch add haptic of_compatible in order to use the haptic
device driver using Devicetree.

Signed-off-by: Jaewon Kim <jaewon02.kim@samsung.com>
Acked-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>