pwm: stm32: Fix error checking for a regmap_read() call

Without first assigning ret, it always evaluates to zero because
otherwise this code isn't reached. So assign the return code of
regmap_read() to ret to make the following error path do something.

This issue was spotted by Coverity.

Reported-by: Kees Bakker <kees@ijzerbout.nl>
Link: https://lore.kernel.org/linux-pwm/b0199625-9dbb-414b-8948-26ad86fd2740@ijzerbout.nl
Fixes: deaba9c ("pwm: stm32: Implementation of the waveform callbacks")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://lore.kernel.org/r/20241003114216.163715-2-u.kleine-koenig@baylibre.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>

Author: ukleinek

drivers/pwm/pwm-stm32.c

@@ -334,7 +334,7 @@ static int stm32_pwm_write_waveform(struct pwm_chip *chip,
 				goto out;
 			}
 
-			regmap_read(priv->regmap, TIM_ARR, &arr);
+			ret = regmap_read(priv->regmap, TIM_ARR, &arr);
 			if (ret)
 				goto out;