regulator: set constraints.apply_uV to 0 in of_get_fixed_voltage_config

Fix fixed regulator using DT failed to call regulator_register.

of_get_regulator_init_data set apply_uV to 1, but fixed regulator
doesn't need it. Set it back to 0.

Signed-off-by: Richard Zhao <richard.zhao@linaro.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>