pwm: Add missing "CONFIG_" prefix

The IS_ENABLED() use was missing the CONFIG_ prefix which would have
lead to skipping this code.

Fixes: 3ad1f3a ("pwm: Implement some checks for lowlevel drivers")
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/core.c

@@ -121,7 +121,7 @@ static int pwm_device_request(struct pwm_device *pwm, const char *label)
 		pwm->chip->ops->get_state(pwm->chip, pwm, &pwm->state);
 		trace_pwm_get(pwm, &pwm->state);
 
-		if (IS_ENABLED(PWM_DEBUG))
+		if (IS_ENABLED(CONFIG_PWM_DEBUG))
 			pwm->last = pwm->state;
 	}