pwm: Add a stub for devm_pwmchip_add()

The devm_pwmchip_add() can be called by a module that optionally
instantiates PWM chip. In the case of CONFIG_PWM=n, the compilation
can't be performed. Hence, add a necessary stub.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Thierry Reding <thierry.reding@gmail.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

include/linux/pwm.h

@@ -478,6 +478,11 @@ static inline int pwmchip_remove(struct pwm_chip *chip)
 	return -EINVAL;
 }
 
+static inline int devm_pwmchip_add(struct device *dev, struct pwm_chip *chip)
+{
+	return -EINVAL;
+}
+
 static inline struct pwm_device *pwm_request_from_chip(struct pwm_chip *chip,
 						       unsigned int index,
 						       const char *label)