pwm: Use guards for export->lock instead of explicity mutex_lock + mutex_unlock

With the compiler caring for unlocking the mutex several functions can
be simplified. Benefit from that.

There is just one caller left for mutex_lock(&export->lock). The code
flow is too complicated there to convert it to the compiler assisted
variant.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://lore.kernel.org/r/210010f2e579a92476462726e18e0135f6854909.1719520143.git.u.kleine-koenig@baylibre.comSigned-off-by: Uwe Kleine-König <ukleinek@kernel.org>

drivers/pwm/core.c

@@ -503,11 +503,11 @@ static ssize_t period_store(struct device *pwm_dev,
 	if (ret)
 		return ret;
 
-	mutex_lock(&export->lock);
+	guard(mutex)(&export->lock);
+
 	pwm_get_state(pwm, &state);
 	state.period = val;
 	ret = pwm_apply_might_sleep(pwm, &state);
-	mutex_unlock(&export->lock);
 
 	return ret ? : size;
 }
@@ -538,11 +538,11 @@ static ssize_t duty_cycle_store(struct device *pwm_dev,
 	if (ret)
 		return ret;
 
-	mutex_lock(&export->lock);
+	guard(mutex)(&export->lock);
+
 	pwm_get_state(pwm, &state);
 	state.duty_cycle = val;
 	ret = pwm_apply_might_sleep(pwm, &state);
-	mutex_unlock(&export->lock);
 
 	return ret ? : size;
 }
@@ -572,7 +572,7 @@ static ssize_t enable_store(struct device *pwm_dev,
 	if (ret)
 		return ret;
 
-	mutex_lock(&export->lock);
+	guard(mutex)(&export->lock);
 
 	pwm_get_state(pwm, &state);
 
@@ -584,14 +584,11 @@ static ssize_t enable_store(struct device *pwm_dev,
 		state.enabled = true;
 		break;
 	default:
-		ret = -EINVAL;
-		goto unlock;
+		return -EINVAL;
 	}
 
 	ret = pwm_apply_might_sleep(pwm, &state);
 
-unlock:
-	mutex_unlock(&export->lock);
 	return ret ? : size;
 }
 
@@ -635,11 +632,11 @@ static ssize_t polarity_store(struct device *pwm_dev,
 	else
 		return -EINVAL;
 
-	mutex_lock(&export->lock);
+	guard(mutex)(&export->lock);
+
 	pwm_get_state(pwm, &state);
 	state.polarity = polarity;
 	ret = pwm_apply_might_sleep(pwm, &state);
-	mutex_unlock(&export->lock);
 
 	return ret ? : size;
 }