mfd: twl6040: Disable and unprepare clk32k in twl6040_power() error path

The clk32k clock is prepared and enabled in twl6040_power() but the clock
is left enabled in case of an error while it should be disable/unprepared.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>