pwm: Don't check pointer for being non-NULL after use

After assigning chip = pwm->chip; the compiler is free to assume that
pwm is non-NULL and so can optimize out the check for pwm against NULL.

While it's probably a programming error to pass a NULL pointer to
pwm_put() this shouldn't be dropped without careful consideration and
wasn't intended.

So assign chip only after the NULL check.
Reported-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/66a6f562-1fdd-4e45-995a-e7995432aa0c@baylibre.com
Fixes: 4c56b143 ("pwm: Add a struct device to struct pwm_chip")
Link: https://lore.kernel.org/r/20240329101648.544155-2-u.kleine-koenig@pengutronix.deReviewed-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

drivers/pwm/core.c

@@ -1525,11 +1525,13 @@ EXPORT_SYMBOL_GPL(pwm_get);
  */
 void pwm_put(struct pwm_device *pwm)
 {
-	struct pwm_chip *chip = pwm->chip;
+	struct pwm_chip *chip;
 
 	if (!pwm)
 		return;
 
+	chip = pwm->chip;
+
 	mutex_lock(&pwm_lock);
 
 	if (!test_and_clear_bit(PWMF_REQUESTED, &pwm->flags)) {