pwm: ab8500: Add error message if pwmchip_add() fails

pwmchip_add() doesn't emit an error message, so add one in the driver.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-ab8500.c

@@ -106,7 +106,7 @@ static int ab8500_pwm_probe(struct platform_device *pdev)
 
 	err = pwmchip_add(&ab8500->chip);
 	if (err < 0)
-		return err;
+		return dev_err_probe(&pdev->dev, err, "Failed to add pwm chip\n");
 
 	dev_dbg(&pdev->dev, "pwm probe successful\n");
 	platform_set_drvdata(pdev, ab8500);