pwm: twl: Really disable twl6030 PWMs

Current twl6030_pwm_disable() implementation writes TWL6030_TOGGLE3_REG
twice, the second write sets TWL6030_PWMXEN bits so the PWM clock does
not disable.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>