pwm: Remove set but not set variable 'pwm'

Fixes gcc '-Wunused-but-set-variable' warning:

	drivers/pwm/pwm-pca9685.c: In function ‘pca9685_pwm_gpio_free’:
	drivers/pwm/pwm-pca9685.c:162:21: warning: variable ‘pwm’ set but not used [-Wunused-but-set-variable]

It is never used, and so can be removed. In that case, hold and release
the lock 'pca->lock' can be removed since nothing will be done between
them.

Fixes: e926b12c ("pwm: Clear chip_data in pwm_put()")
Signed-off-by: yu kuai <yukuai3@huawei.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-pca9685.c

@@ -159,13 +159,9 @@ static void pca9685_pwm_gpio_set(struct gpio_chip *gpio, unsigned int offset,
 static void pca9685_pwm_gpio_free(struct gpio_chip *gpio, unsigned int offset)
 {
 	struct pca9685 *pca = gpiochip_get_data(gpio);
-	struct pwm_device *pwm;
 
 	pca9685_pwm_gpio_set(gpio, offset, 0);
 	pm_runtime_put(pca->chip.dev);
-	mutex_lock(&pca->lock);
-	pwm = &pca->chip.pwms[offset];
-	mutex_unlock(&pca->lock);
 }
 
 static int pca9685_pwm_gpio_get_direction(struct gpio_chip *chip,