iio: adc: ad7944: Convert to use pwm_apply_state()

pwm_config() is an old API function that isn't recommended any more.
This driver is a prime example for the reason: Either you need more than
one function call (and so several hardware parameter calculations and
several hardware modifications resulting in more glitches than usally
necessary) or you have to rely on previous hardware state (here: that
the PWM is enabled, because the driver doesn't ensure proper operation
if the PWM happens to be disabled).

Convert to pwm_apply_state() which is the designated replacement without
these disadvantages.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>

Author: ukleinek

drivers/iio/adc/ad7944.c

@@ -426,7 +426,7 @@ static ssize_t ad7944_sampling_frequency_store(struct device *dev,
 {
 	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
 	struct ad7944_adc *adc = iio_priv(indio_dev);
-	u64 period_ns;
+	struct pwm_state sample_state;
 	u32 val;
 	int ret;
 
@@ -440,9 +440,12 @@ static ssize_t ad7944_sampling_frequency_store(struct device *dev,
 	if (val == 0)
 		return -EINVAL;
 
-	period_ns = div_u64(NSEC_PER_SEC, val);
+	pwm_init_state(adc->pwm, &sample_state);
+	sample_state.period = div_u64(NSEC_PER_SEC, val);
+	sample_state.duty_cycle = AD7944_PWM_TRIGGER_DUTY_CYCLE_NS;
+	sample_state.enabled = true;
 
-	ret = pwm_config(adc->pwm, AD7944_PWM_TRIGGER_DUTY_CYCLE_NS, period_ns);
+	ret = pwm_apply_state(adc->pwm, &sample_state);
 	if (ret)
 		return ret;