mfd: rk808: RK818 uses DEV_OFF to power off supplies

DEV_OFF and DEV_OFF_RST functions for RK808 are designed error that
only DEV_OFF_RST can power off supplies. RK818 has been fixed this
issue, so that DEV_OFF is used to power off supplies.

Signed-off-by: Jianhong Chen <chenjh@rock-chips.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>