Input: regulator-haptic - simplify code

All the use cases in this driver has a regulator_haptic_toggle() call after
regulator_haptic_set_voltage(). So make regulator_haptic_set_voltage() call
regulator_haptic_toggle() to simplify the code.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>