If the zero duty cycle doesn't correspond to any voltage in the voltage
table, the PWM regulator returns an -EINVAL from get_voltage_sel() which
results in the core erroring out with a "failed to get the current
voltage" and ending up not applying the machine constraints.
Instead, return -ENOTRECOVERABLE which makes the core set the voltage
since it's at an unknown value.
For example, with this device tree:
	fooregulator {
		compatible = "pwm-regulator";
		pwms = <&foopwm 0 100000>;
		regulator-min-microvolt = <
2250000>;
		regulator-max-microvolt = <
2250000>;
		regulator-name = "fooregulator";
		regulator-always-on;
		regulator-boot-on;
		voltage-table = <
2250000 30>;
	};
Before this patch:
  fooregulator: failed to get the current voltage(-22)
After this patch:
  fooregulator: Setting 
2250000-2250000uV
  fooregulator: 2250 mV
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Link: https://lore.kernel.org/r/20200902130952.24880-1-vincent.whitchurch@axis.com
Signed-off-by: Mark Brown <broonie@kernel.org>
                return ret;
        }
 
-       drvdata->state                  = -EINVAL;
+       drvdata->state                  = -ENOTRECOVERABLE;
        drvdata->duty_cycle_table       = duty_cycle_table;
        drvdata->desc.ops = &pwm_regulator_voltage_table_ops;
        drvdata->desc.n_voltages        = length / sizeof(*duty_cycle_table);